Release file lock handle

I have some servers, they act as file servers. They contain lot of EXE files and workstations (XP) run apps from it

\\SERVER1\Files\Project.exe

Till now Servers was running samba (linux) and I was able to delete the Project.exe or replace it with a new file, even if workstations are executing it.

Now, on Windows 2003 Server, of course the file cant be deleted because "its already in use by another process" and Im looking a way to release the file lock handle so I can overwrite the file, without the need of restarting the server.

Does anyone has a utility/way/dll or anything else that will help me to do this? Everything is automatic (no human actions), so something that can work in command line.

Thank you!