I am assuming a relatively small wokgroup of around 10-25 users, in the absence of other information. There are possibly two issues here, an easy one and a difficult one. The easy one is to throw RAM at the problem – double the quantities on the workstations and quadruple on the server. You might also upgrade your switch/router connected to the server to gigabit and cables to cat 6 (5a at a pinch, but this degrades performance to around 300MB/s I understand) if it is not already, as you will not be gaining the benefit of gigabit on the server unless you do.
The hard part is the database. Access databases (from 2000 on if I recall) can be configured in one of two ways – one way is a monolithic entity, in which queries to the data generate significant traffic across the network because large chunks of database code are shuttled across the network along with the data, abd the other way is a client-server mode, (using a technology MS calls MSDE), in which the processing is done on the server, and only the query instructions and the data results are streamed over the connection, displaying the results on your desktop in a separate “front end” to the database.
I am not a DBA, so I cannot tell you how hard it is to convert one type to the other if your “stuck with” database is a monolithic one. Perhaps a DBA in the forum can help if that turns out to be a problem. In any event throwing RAM at the problem will solve a lot of ills in the database world.