I'm not sure in Windows 7, but in XP SP3 it is an option in the Boot Camp item under Control Panel. After you install all the junk from the OSX DVD, there should be a Boot Camp icon in the Control Panel (should look like this). There is a "Keyboard" or "Mouse" tab in there which will give you the options for tapping, right-tapping, multi-touch, etc.
Should look something like this:
alt text http://imagebin.org/index.php?mode=image&id=56552
Update
It seems that this solution is only available with the newer unibody MacBook Pros, and may not work for everyone. Check out the comments thread for more info.