locked file issues

Our server runs 2000 and various machines in the office
run XP Pro or 98 or 2000. We are frequently having issues
with file maint. When we try to delete a file it will act
as if it has deleted it but it continues to pop up as
soon as you come back to the directory. If you try from
another machine it says the file is locked or in use. If
I bring the file server down and back up it will usually
correct itself but I would have to do that several times
a day to fix this issue. It also occurs when we try and
open documents we have had opened earlier in the day. It
will say the file is locked and in use. Any suggestions
or solutions out there? It's like a really big time delay
in the server knowing the true status of the file.