You are pushing it with 1 gb as vista has been reported to use around 700mb of ram on it's own, considering that many games use more memory than that then i would say you need more ram.
Another potential problem may arise with your video card, I'm assuming it's a nvidia card using turbo cache, these aren't very good for playing games. You may find that with your current graphics card you will have to turn down the settings to et your games to play, most recent titles will struggle if they play at all. You have a good processor, consider pairing it with a better graphics card and another 1gb of ram for playing games. Here is a link which provides information on pc hardware.
http://tomshardware.co.uk/ And another comparing the performance of available graphics cards, you can select the games and compare cards against each other: