this is what happens to me, although you'll never convince me it is a problem with me not having enough memory since I am able to easily run CoD4, Half Life 2, Portal, and other games at 1920x1200.
I know it does, you can have 8GB of memory, none of my games lag at all, the problem lies in Vista.
Longshot, but go onto a flash enabled site, e.g. youtube. Right click on any flash content. Select settings. Go through the tabs. Disable hardware acceleration. This seems to be a bug in vista.