Test Access Database
This is an access application that allows you to view what computers are currently connected to other access databases.
Alternatively, you could just look at the LDB file that access creates, and contact each of those people to see who actually has it open... But since I've done the work, why not reap the benefits? =)
This definitely works for Access 2003. I'm not sure about other versions...
If you just have one problem database, you can also pull the code from this application to
auto-close the database when you go in and set a flag on a table.