In addition to what TEWS said, I'd add that what you should do is get the latest drivers from the manufacturer - do not rely on the ones that Windows 7 loads in. There have been some reports that thrie drivers for various components are either not the latest or don't work quite right.
The IBM site - Lenovo Support & downloads - Drivers and software - ThinkPad X61, X61s
has video drivers for Vista that should work. If they don't run right "out of the box", do the following:
•Unzip the software
•Right click properties on the “setup.exe”
•Click on the Compatibility tab and select mode to “Windows Vista Service Pack 2″ and select “run this program as an administrator” at “privilege level”
•Run the setup and reboot
Hope this helps. If you still have problems, we'll all be here...