I must say, if you have not used Unlocker you need too!
IF:

• Cannot delete folder: It is being used by another person or program
• Cannot delete file: Access is denied
• There has been a sharing violation.
• The source or destination file may be in use.
• The file is in use by another program or user.
• Make sure the disk is not full or write-protected and that the file is not currently in use.

http://ccollomb.free.fr/unlocker/