In Windows XP, hundreds of megabytes are stored in the C:\Windows\Sytem32\dllcache folder by the Windows File Protection feature. You can save a lot of disk space by simply deleting all the contents and setting a limit on the folder size. In Windows Vista, this feature is called Windows Resource Protection. After a while, WRP can contains thousands of megabytes of files since there is no file size limit set. You can limit the amount of space dedicated to this feature though by using the Group Policy editor. Click on the Start button and type 'gpedit.msc'. Navigate to 'Computer Configuration\Administrative Templates\System\Windows File Protection'. In the right-hand pane, double-click the item named 'Limit Windows File Protection cache size'. Set its status to 'Enabled', and fill in the desired cache-size limit in megabytes.