What types of games do you play?
For FPSs or RTSs the PC is utterly dominant. If your big thing is either or some combination of those two pick yourself up a new vid card.
For racers, sports titles, fighting games, adventure games or platformer/hybrids the consoles are utterly dominant. If your big thing is a combination of those then pick up a XBox.
Between myself, my wife and my kids we have two XBoxs, three Cubes and a PS2(along with my rig, AXP 2500+/R9800Pro). I've been gaming a lot more on the PC lately mainly because the games I want to play are on the PC. Oddly enough, three of the games I've been sinking time in to on the PC are titles I already own on the XBox that are just plain better on the PC- Morrowind(DO NOT buy this for the XBox, buggiest console game ever by a long shot), KoTOR and Halo. The PC has superior visuals if you have the rig to push them, and for first person mouse/keyboard still owns.
If I was in your spot I would buy a XBox, but I really don't like the idea of any game coming out and not being able to play it. After I clear off my stack of PC games I'm trying to play through at least one of the XBoxs should be open so I can focus on the titles for that I've been meaning to get throug(Prince of Persia, Simpsons Hit&Run and Beyond Good&Evil are sitting here, my wife has played through all of them and the kids are working on them now).