vista or xp to play

That is my config:

Core 2 Duo E8500
Asus P5K-deluxe
-2 * 1GB Corsair PC8500 dominator
MSI 8800GTS-OC

At the moment I have XP Pro and I wonder whether it is best kept to xp or vista 32bit SP1 with 4GB of RAM.
With what OS I better performance?
With vista I 4GB recognized and DirectX 10.

I think it would be preferable to retain XP.
Vista will not change much at the interface of used games.
Also before embarking on a mutation of XP to Vista, you are strongly advised to check that there are compatible drivers for all devices installed.
This is the major problem faced by all those who seek a transfer of this kind.

what plays in the flow of games,
speed proc
volume RAM
volume video card memory
and ventilation system of trial and the video card

If you change Instead Vista 64.
With your config you have no problem with drivers.
With Vista 32 you can use only 3.2 GB of RAM. That's enough for current games but I think that soon this will no longer be the case.
Vista does not bring you change in the interface of games but DX 10.

if you can get 4GB with Vista 32 but SP1

Otherwise yes Vista 64 / Direct 10, and 4GB of RAM will be apreciables.
Once streamlined services, indexing, so scheduled tasks.

The big flat with vista (32 or 64) is the disappearance of materials that allowed Profiles in XP to simmer an OS surprise performance in games by playing drastically on services, drivers and patches of funds unnecessary in this scenario .