I think his question is, "I have heard Vista is a resource hog and running the same games (that I do on XP) will be slower in Vista than it was in XP."
I would wait for a 'Vista vs XP Gaming Performance' (using the same hardware) comparison that lots of sites will inevitably carry come January 30th. And I'm thinking it won't look good for a little while thanks to immature drivers. But it will be deal-breaker bad, I have no idea.
If you meant what DirectX 10 will do for gaming. this is just my personal opinion but DirectX 9 wasn't fully exploited until Half-Life 2 showed up in 2004...and we know what Oblivion did for DirectX 9 in 2006. So far, most DX10-ready games look like they will ship with DirectX 9 rendering with maybe a patch released later - that will probably add a few superficial tweaks here and there (think the Far Cry SM 3.0 patch).
What kind of games do you play? The PC has lots of quality FPS and RTS games (that don't feel that great on a console). And Sony-exclusive games you like? Because apart from few notable exceptions (I think PS3 and Gran Turismo comes to mind), the industry does seem headed for cross-platform games. I would personally go for the PC route.