I just built my first computer a few months back, so here's my .02:
I think you first need to figure out what type of CPU you want. p4, athlon 64, whatever. you can do some research to figure out what works best for you, but my guess is that "anything decent" will do. no need to go crazy. I went with a p4. safe choice I guess.
Then pick a motherboard that will fit your chip. don't skimp on the motherboard, as this will determine how much flexibility/expandability you have. make you you get at least 2 slots for RAM, preferably more, so it's easier to go above 1GB. sounds like you'll want lots of firewire/USB ports. also, I think you want ATX form factor, unless you have limited space for your PC. I bought
this one. no complaints. also, for more firewire/usb ports, it's very easy to buy an expansion card.
buying ram is pretty easy. I would just guy ahead and buy 1gb of dual channel RAM. not very expensive, and it should be all you need for a while.
I'm not an expert on video cards, so I can't so too much about them. like you already know, just be sure to buy 1 w/ 2 DVI's. there are some with 4, but they are quite expensive. again, it doesn't sound like you need anything too schmancy - just make sure it's AGP or pci express/compatible with your mobo, and anything mid-range you find at newegg.com should be fine. also, do you want a TV tuner?
if you feel like kicking it up a notch, you could install 2 hardrives; a fast one dedicated to windows, and a big ole regular one for everything else.
one thing you will need (duh): software. shop around for good windows/office deals, as they can be expensive. or you could go a less ethical route. your call.
finally, I would buy a full size atx tower with at least 400w of power. as this is your first time building one, having a lot of room inside to work around will help you out.
gl