http://www.pcworld.com/downloads/file/fid,70551-page,1-c,utilities/description.html

If Windows won't let you manually delete a program file or folder, try Cedrick Collomb's free Unlocker. Once installed, Unlocker comes up automatically when Windows refuses to delete, move, or rename a file or folder, or you can launch it from the file or folder's context menu. Once up, it shows you what processes are hanging onto the culprit and lets you kill them.