I'm running Windows 7 X64 on a much weaker laptop than yours. It's fine. It also originally came with Vista. The hardware requirements of Win7 are similar to Vista; I've never read of a Vista machine that couldn't run Win7.
It sounds like your Windows installation is corrupt. If you did an upgrade-in-place from Vista, you might consider doing a clean install instead. More easily said than done, but it's batter than limping along with a semi-broken OS.