Hey! I've got a pastor father too, but thankfully my atheism doesn't seem to be a big deal for him. (It helps that I don't live nearby.)
I think the "conflicting belief system" is, as I understand it, the right model. There's a Christian worldview, which has some basic assumptions (God exists, the Bible is a useful source for learning about God, etc.), and there's a reductionist worldview, which has some basic assumptions (everything can be reduced to smaller parts, experiments are a useful source for learning about reality, etc.), and the picture you can build out of the reductionist worldview matches the world better than the picture you can build out of the Christian worldview. (There are, of course, other possible worldviews.)
I would not put much hope into being able to convince the people at this event that they should be atheists; I wouldn't even hope to convince them that you should be an atheist. And so the question becomes what your goals are.
If you're concerned about recanting your atheism and meaning it, the main thing I can think of that might be helpful is the how to change your mind sequence. You can keep that model in mind and compare the experience you're undergoing to it- it's unlikely that they'll be using rational means of persuasion, and you can point out the difference.
Are there people I can be put in touch with, or online meetups where I can talk to people and arm myself? Should I start a discussion post, or what? I'm unfamiliar with the site structure here, so I could use some help.
Starting a post in discussion is an alright idea; it'll work well if you mention specific arguments that you want to have responses to.
A few notes about the site mechanics
A few notes about the community
If English is not your first language, don't let that make you afraid to post or comment. You can get English help on Discussion- or Main-level posts by sending a PM to one of the following users (use the "send message" link on the upper right of their user page). Either put the text of the post in the PM, or just say that you'd like English help and you'll get a response with an email address.
* Normal_Anomaly
* Randaly
* shokwave
* Barry Cotter
A note for theists: you will find the Less Wrong community to be predominantly atheist, though not completely so, and most of us are genuinely respectful of religious people who keep the usual community norms. It's worth saying that we might think religion is off-topic in some places where you think it's on-topic, so be thoughtful about where and how you start explicitly talking about it; some of us are happy to talk about religion, some of us aren't interested. Bear in mind that many of us really, truly have given full consideration to theistic claims and found them to be false, so starting with the most common arguments is pretty likely just to annoy people. Anyhow, it's absolutely OK to mention that you're religious in your welcome post and to invite a discussion there.
A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site.
(Note from orthonormal: MBlume and other contributors wrote the original version of this welcome message, and I've stolen heavily from it.)