So I don't know enough about virtual machines to make a good recommendation (you should go to Superuser.com for that), but I did have some success with using VirtualBox.
I've run a large number of games on Virtual Machines, dating back to running Warcraft 2 on OS7 (which I don't recommend btw). Over time I've learned two important rules:
- Don't play anything with timing is a factor (stick to turn based)
- Have something else to do (you may be waiting a while between turns)
While you can run games of that nature they're going to perform at a much slower rate. For some games you can pull this off (eg. Civilization). For others its just going to be painful (ie. in college I had a bad experience with WoW on VM). The factors which largely affect this are:
- AI time (AI burns a ton of CPU so if its slow already...)
- Graphics time (I don't mean GPU, I mean more like physics engines and water simulators)
- Number of Moving Parts (more = worse)
- Latency (if you're playing over internet most games continue even when you slow down)
Try to keep these in mind. While it is feasible, it can often be painful. You might also want to examine why you're using a VM, especially when most of those games already run on Win7...