If your server is doing backups I'd store it there. That way if a computer crashes you don't really lose it and assuming that all these users are using different computers, they can still access it.
Check out under the tools - workgroups.
You create a workgroup for that database file. Then each person who is going to use it have them JOIN that workgroup. That should enable the capability to have multiple people in the database at the same time. If not, each person will have it locked under administrator I believe.