Need hardware advice

[jenkitty]

So, I'm accepting a Stafford loan for school, and one of the things I can do with the money is purchase a computer. I think I'd like to build my own, so I need advice on hardware. No, I will NOT get a laptop, I hate them with a passion and will only use them if I have to. The screens are too small and the keyboards and mice hurt my hands.

What I'd like in a computer...

1. Runs some version of Ubuntu Linux.
2. Sound and video support, enough to handle, say, YouTube videos and sound editing with Audacity.
3. Memory and motherboard capacity to handle the above.

I'm not a heavy graphics gamer and I don't do video editing. I just want to be able to do my music editing for my burlesque, watch a DVD, surf the Web for school and pleasure, and write papers and whatnot for my classes. A printer would be nice, too. So, what do I need?

What size/type/brand motherboard? How much memory? Brand recommendations? Sound and video card suggestions? Compatible hard drive for all this? Anything else I should know?

Oh, and I'd be budgeting for a 2 gig memory stick as well, for transporting said papers, etc., if I'm going to carry them around.

Edit: Am I just better off buying some preassembled thing from Newegg or somebody?