If you have Windows XP, system restore also can take up to 12% of your hard drive space. You can eithe delete all the restore points except the most recent, or delete them al and disable system restore.
To delete everything except the most recent, run the Disk Cleanup utility, go to the "more options" tab, and where it says "system restore", click the cleanup button.
Or to disable system restore and remove all restore points, go to Start > All Programs > Acessories > System Tools > System Restore > System Restore Settings > Then disable system restore on the drives you wish.
What you also may want to do (and i find this very useful), is go to the search option in Windows, dont type anything in and just let it show you all the files on your computer. Then order it by largest size, and there may be some very large files that you dont need, and that you could delete.