I installed a virtuall machine just as a last resort to try out older games that have some problems on win 7.
I really dont use it that often because I have found other sollutions allong the way to get them running inside my OS.
I have to say that the virtuall machine I have (VMLite) didnt support directdraw and I have to run SC4 in software mode.
It tend to run games that have graphics problems in win7, usually if you have a nvidia card.
My computer is pretty fast and I have lots of ram (6 GB) and ram helps when running VM as it uses as much ram as
you allocate to it and more is better.
So VM is a last resort but you can at least play a lot of older games in it that have compatibility issues with win7.