FSB? PCIe? AGP? DDR400OMGWTFBBQ! PC parts/construction questions

JerikTelorian

So, I applied for a grant at my school to do some research over summer. I'm not sure if I got it (and won't for a few weeks), but I've decided I could use some of the money, along with my summer income, to begin building a new PC.

So, I trot along to Pricewatch.com, and take a look at the new Pentium D packages (Because I hear there's no point building a machine without dual core) with mainboards and coolers.

And heres where I realize I have no clue what I'm looking for.

It's not that I'm not tech savvy- my job at school is tech assistance. Thing is, most, like, 99% of my job is software stuff. I have a confident knowledge in basic PC hardware repair and have even put one or two PC's together, but I had a mainboard and power supply to start from, so I never really learned any of that.

So, I need some advice on the important numbers. Here's a few questions I have; keep in mind that I have no real parts (other than peripherals like keyboards/mice) lying around, so I'd prefer to get sockets and stuff that are up-and-comming, assuming they aren't a huge pricegouge.

1. How on earth do I decide what kind of mainboard I want? I know well enough I need a socket 775 board to fit the dual-core chip, but what about everything else. An 800mHz FSB seems to be common, is that an acceptable rate?
2. AGP8x or PCI-e16? My friend's PC has PCI, I've had AGP in every PC I've owned. Which one is the bigger name? I thought PCI-e was replacing AGP, but on the boards I'm seeing, they only have AGP8x. Is this just because they are the cheap models?
3. Power Supplies: What about them? This is a realm of which I know nothing.
4. RAM: My current laptop uses DDR2-333mHz, but I'll bet that's gone up. Planning ahead for Vista, would it be wise to look at a DDR-400mHz 4gb mainboard, or is that too shallow to prep for the future?
5. Would I be wiser buying a bare bones case somewhere, and filling in the holes, or buying everything myself separately? I have the opportunity to buy stuff both online, and at a monthly (or so) computer show/sale in my hometown where both styles of items would be available. My main goal with this machine is to build something that I can maintain over a significant period of time.

I'm not looking for a NASA-Supercomputer, but I'd like to assemble a decent, and most importantly versatile gaming rig. I hear Physics cards aren't really worth the purchase yet, so that wasn't part of my purchasing goal yet (unless I'm mistaken about them). I do plan to run Vista Ultimate on it at some point, since I may be getting a fairly discounted copy of Vista as part of my job.