Try this site. I found this by searching Google for "
monitor calibration". It won't change anything on your PC, but it will show you the difference between your current configuration and a calibrated configuration.
There's a tool that comes with Adobe Photoshop called Adobe Gamma which is used to change the color / gamma settings on your PC to match "real" colors. If you have Photoshop installed, you should be able to find the shortcut in the Start menu.
If you don't have Adobe Gamma,
this site offers a link to an alternative.