Dunno if this is any good but adobe have a basic gamma callibration tool that comes with photoshop if you have it.
edit:What about this:
http://www.easyrgb.com/calibrate.php
or
http://www.photoscientia.co.uk/Gamma.htm
Gamma 2.2 is supposed to be a good chart for windows users.
What monitor is it by the way??