I have two suggestions.
The easy cheat.
Give access not to the original database, you can even password protect
it, and make a copy for everyone else to use. If they change something, no
problem the next time you copy the original over the copy it all goes away.
I have my applications using this updated every morning when I log into my
computer by a bat file dos copy command.
Don't ask why I have to do it this way.
The other, some will say better, way is to activate Microsoft Access
Security. This is a great feature and very powerful, however it also has
one of the steepest learning curves known to man. An error in setting
things up can lock not only other uses out, but you and God as well. Read
the instructions many times before trying it and practice on some test
programs first.
It is a bother, but it really is worth it.
You can start here
http://support.microsoft.com/default.aspx?scid=kb;[LN];207793