OK, I'll have a go at Tristan Ewins' questions (mainly because they're more interesting than the strawman atheism of GP's article).

Easiest first: " why do we assume that materialism and determinism necessarily have a monopoly as 'credible science'?"
(A) Materialism- Because, by definition, science has to deal with the observable. You might as well ask why an apple tree doesn't produce peaches (ie if it produced peaches it would be a peach tree). Science does not deal with the "transcendent", leaving it to theologians and philosophers.
(B) Determinism- I suggest some reading on quantum mechanics and chaos theory before suggesting that all science is deterministic. Much of modern physics is now probabilistic.

"How is it possible to understand free will, consciousness and sentience on materialist and determinist grounds? How is it possible to explain such phenomena except by resort to the 'transcendent'?" By transcendent I presume you mean the agency of God? If so, why do you believe that sentience couldn't arise without divine intervention. I don't believe brain function has anything that distinguishes it from any other physical function of the body (except for its complexity). The brain is a physical organ, though we don't fully understand its workings. Our emotions, language and reason are remarkably well-developed, but where's the evidence that this is the result of theistic interference?

Consciousness and sentience are not "transcendent" they are "emergent".

For all its flaws, The Happiness Hypothesis by Jonathan Haidt http://www.happinesshypothesis.com is a good read, filled with neat observations:

“When the moral history of the 1990s is written, it might be titled ‘Desperately Seeking Satan.’ With peace and harmony ascendant, Americans seemed to be searching for substitute villains. We tried drug dealers (but then the crack epidemic waned) and child abductors (who are usually one of the parents). The cultural right vilified homosexuals; the left vilified racists and homophobes. As I thought about these various villains, including the older villains of communism and Satan himself, I realised that most of them share three properties: They are invisible (you can’t identify the evil one from appearance alone); their evil spreads by contagion, making it vital to protect impressionable young people from infection (for example from communist ideas, homosexual teachers, or stereotypes on television); and the villains can be defeated only if we all putt together as a team. It became clear to me that people want to believe they are on a mission from God, or that they are fighting for some more secular good (animals, fetuses, women’s rights), and you can’t have much of a mission without good allies and a good enemy.

The problem of evil has bedevilled many religions since their birth. If God is all good and powerful, either he allows evil to flourish (which means he is not all good), or else he struggles against evil (which means he is not all powerful).” (page 72)

I think Graham Preston needs to look around and note that everywhere atheists are managing to live worthy lives. Also, “higher rates of belief in and worship of a creator correlate with higher rates of homicide, juvenile and early adult mortality, STD infection rates, teen pregnancy, and abortion in the prosperous democracies.” http://moses.creighton.edu/JRS/2005/2005-11.html

Conversely, atheism may be associated with higher rates of suicide http://ajp.psychiatryonline.org/cgi/content/abstract/161/12/2303

It seems to me that rather than making polemical claims about the moral vacuity of atheists, a more “moral” approach would be to admit that both believers and non-believers can learn much from each other.

A response to Mr. Preston’s view that atheism leads to nihilism.
Some Philosophy:

Not withstanding John Mackie’s (that’s where this view originates) view that moral values must be queer things, there is no persuasive reason for thinking that moral values are anything other than natural features of the natural world. A detailed discussion of why Mackie is mistaken is probably not appropriate for this forum but readers who are really interested might try Russ Shafer-Landau’s book Whatever happened to Good and Evil? In the meantime here is something to think about.
1. Language is a natural property of the universe, it exists among human beings who are themselves a part of the natural universe. Language (in the ordinary sense of the word) does not exist among protons and electrons. Language is a property of entire organisms not their component parts.
2. Language is universal. All human societies have some form of language.
3. Particular languages are not universal. Different societies have different languages despite the fact that all human beings have the same speech-making anatomy.

In other words, there can be characteristics of the natural world that are not properties of the component elements of the natural world (but entire entities) and these characteristic can be universal without invariable generating universal agreement. I am not suggesting that moral value is reducible to language but there is no good reason for thinking moral values are not part of the natural world simply because they don’t exist in electrons etc.

Nor does disagreement about moral values itself indicate that there are no universal moral values or that there has been no progress in gaining agreement on such values.

If one is an Externalist about moral value, disagreement is not problematic. One can simply be mistaken about one’s moral values – because one is mistaken about matters of fact and/or irrational. Given the tendency of human beings to be guilty of both mistakes, it is only surprising that there is not more disagreement.

In short, there is no good reason to believe that an atheist must be committed to moral nihilism

A correction:
"Determinism means we have no control over what we do, say, or think - no matter how much it feels that we do to the contrary." - G Preston.

Err actually, this is not what Determinism means -the logical problem here is the phrase "we have no control" which is entirely ambigious. If it were literally true that I have "NO" control then there would be no differance between a compulsion and ordinary behaviour. But there typically is - a person suffering complusions typically wants not to suffer them. On the other hand - the fact that I cannot will the development of Neurons does stop me identifying with the thoughts that are the product of Neurons (it is not even clear what that would mean)

Again I would suggest that the problem here is the tendency to confuse the what happens at the level of component parts, with what happens to the entire organism. - Hard Determinism is excessively reductive and most likely false. Soft Determinism is probably true and is quite compatible with our ordinary sense of freewill - (although not with some metaphysical understandings)

This will sound very simplistic after all the erudite responses so far but here goes.

My two children are in the unenviable position of having a non-believing father whom feels it is okay to let them both attend a pentecostal church run by his brother-in-law.

The only trade off is that when possible we sit down and read through the bible together and discuss what it reveals.

Last year when wading our way through Genesis (an excellent teaching tool) we talked through the issues posed by Abraham's willingness to sacrifice his own son to show his submission to God's will. We concluded that sin and morality can be two different things. If their pastor/uncle was to walk past them one day with his son in tow, clutching a knife and voicing the conviction he was off to do God's bidding then what would their response be? If they followed their moral convictions then they would do all within their power to stop him even though this would in effect be sinning if it was indeed God's will.

This is of course an extreme example but thankfully both my children were very firm about being prepared to act morally instead of sinlessly.

When you hold most of the other Genesis figures up to similar scrutiny they are far from being shining examples of piety and one can not help but get the sense that this may well be what the authors intended. Could it be that our religions serve to elucidate human morals rather than the other way around?

Genesis has been a brilliant resource and many nights of meaningful discussion have taken place as we have been making our way through it. I can highly recommend it to those of all persuasions.