A few days ago I wanted to delete a file (in Windows XP) but an error appeared: ‘File in use’ error.  The classic Windows Task Manager won’t provide any info regarding which file is used by which process.

As I had no idea what process was using my file I’ve googled and I’ve found a neat free program called Process Explorer.
There with just a simple search I’ve found that my file was used by whatever.exe. Killed the process and deleted the file. Simple and easy.