Some older games will not work in Windows 7. You can check the Compatibility Center to see if your specific games are compatible with Windows 7. Just select "software" and type in the name of your game - http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx
If you have Windows 7 Professional or Ultimate you can run your games in XP Mode. This will make games that are designed for XP, also work with Windows 7.
Additionally, take a look at http://windows.microsoft.com/en-US/windows7/Fixing-game-performance-problems
and see if any of the tips help to fix the problem.
Microsoft Windows Outreach