xls file locks on server through network - file accessed by multiple users

[Tim Smith]

I have xls files on server accessed by multiple users
through a network. We just upgraded to Office XP. New
problem introduced with upgrade. Frequently, after the
user of the file (that has write access) saves and exits
the xls file, the file still shows that user as owning
it, even if they are logged off there system.
Subsequently all users can only access the file as "read-
only" or they can't access it at all.