WinSxs Folder Cleanup
Here are some options you may consider to clear up disk space – some routine and some extreme:
Run Disk Cleanup tool or CCleaner
Uninstall unused applications
Move Page file to another drive
Use the dedicated dump file option to capture memory dump files on another volume on the system.
Disable system restore points
Offload user profile and program file directories to another volume on the system.
Further to Brett's post, I thought I'd share the above. Taken from http://www.winvistaclub.com/f16.html