I am most likely going with vista.
I mainly game on my computer. But I like being able to do many things at a time if possible. For instance playing some game which lately has been **** with the crappy rig, browsing the web, listening to music, talking via skype, torrenting, and possibly running some other programs. With the new games, multitasking is impossible, and even running a hl2 game is taking it's toll, regardless of what else is going.