PC CDs to work on Macs

Is it possible at all to have games that are only PC compatible to work on Macs? Is there some kind of program I can download to convert it? I just switched to a Mac and I don’t want to have to buy all new games.

If you’re using an Intel-based Mac, you can install Parallels and a copy of Windows XP (i’m not sure that Vista works with Parallels)