Well, Vista definately has its problems, but when it comes to minimizing graghically intense games, the game can, a lot of times, be causing the problem itself. I just wanted to let you know this, with a little proof: I have a XPS Gaming laptop, and depending on the game, it might crash when i try to alt-tab out or minimize it. Some game developers even manage to disable these default Windows shortcuts so you can't switch applications while gaming, I am assuming because they foresee the problems it might cause with stability. Also, games sometimes do not re-utilize the video card correctly, and will either lag badly when returning to the game, or crash.
Solution: Not all graphically intense games can be minimized, even on the most expensive and powerful gaming machines. You can do what I do, which is remember which games work fine with switching applications and which ones don't.
(I am refering to <ALT> + <TAB> out of full screen games here)