File in use while trying to save a docment

Don't know if this a Vista or Office 2007 problem so that is why I am
posting it here. I work at a college. Three of us in our IT
department are running Vista and Office 2007. Sometimes while working
on a document (2003 format) we go to save it and it says file is in
use by another process. If we go to another machine that is running
Windows XP and Office 2003 we can open the file make changes and save
it with no problems. Any one have these kind of problems? Any help
would be appreciated.