If your system is stable and are not going to uninstall IE8 you can delete lots of junk left by IE7.
Delete folder C:\WINDOWS\IE7 (contains IE6 to IE7 update rollback files)
Delete folder C:\WINDOWS\IE8 (contains IE7 to IE8 update rollback files)
Delete folder C:\WINDOWS\IE7Updates (contains IE7 security patches rollback files)
Delete all folders from C:\WINDOWS\$hf_mig$ which include IE7 in their name
Registry: delete all keys under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows XP\SP0 which include IE7 in their name. If you have had all IE7 patches installed these keys contains total of several thousand values and will free up more than 500kb data from registry.
This cleanup is also pretty easy to do manually if this doesn't make into CCleaner. CCLeaner philosophy seems to be more like that every patch/servicepack should be uninstallable forever instead of 'make all patches permanent after x-months of stable use'. But ill post this here anyway
