Hey, thanks for the replies.
And no, you cant add stuff to an Xbox 360. Actually, you can... but thats a whole other mess.
I'm selling it to get money so I can build a 1600 dollar gaming computer instead of a 1000 dollar gaming computer. I bought the 360 as an extreme budget computer thinking I would be able to play any game I wanted to on there if I wanted good graphics. Little did I consider that I like MMORPGs and not much of anything else... and the only MMOPRG for the Xbox 360 sucks and its gunna be another two years until a half decent one comes out. Big mistake, hopefully I dont miss much.
I dont know what I'll get with the upgrade... probably a better motherboard, power supply, perhaps a sound card also. And some 7.1 speakers to go with it.