I frequently get into the situation of having files locked (in Windows mostly) when I am doing development. I bet that has happened to everyone at one time or another and it can be a pain since Windows does not offer a quick method to simply unlock the file(s) in question from Explorer (how shortsighted is that? I wonder if Win7 is going to have that feature?).
Anyway, I discovered the freeware Unlocker by Cedrick ‘NITCH’ Collomb one day and have been using it every since. Simply right click on the Folder or File(s) in question and click on the Unlocker shell extension and you will have a list of programs that are locking what you selected – nice and easy.