Windows 7 and Windows 2008 R2 include a cool feature as part of the disk cleanup wizard that allows you to remove old service pack backup files to free up space on your C: drive / partition. Unfortunately it means installing the Desktop Experience which, besides having a bunch of crap you don't need, requires a reboot.
There is another (and better) way!
Simply copy cleanmgr.exe to C:\Windows\System32. from-
and copy cleanmgr.exe.mui to C:\Windows\System32\en-US.
(You can also just go into C:\windows\winsxs and search for those two files.)
Now you can simply run cleanmgr.exe (you may need to navigate to it and run as administrator if you have UAC turned on) and select "Service Pack Backup Files".