Sometimes you are stuck by not able to delete the file because some application unknown
to you is holding the file lock. This freeware (Unlocker)
helps you in those scenarios. I haven't tried it yet, use it at your own risk !
What looked impressive for me is the GUI listing of all applications having locks
over files in a folder.
Read the complete post at http://www.venkatarangan.com/blog/2007/11/27/Unlocker.aspx