This should cover it pretty well:

http://home.bendbroadband.com/conradsystems/accessjunkie/splitting.html

Bear in mind that splitting a database is not meant as a cure for bigness,
fatness or slowness. Each of those symptoms may have one or more causes,
but none will be helped by a FE/BE split. You may find that it runs slower
afterwards than before.

Which is not to say that you shouln't split it - quite the reverse. The
purpose of splitting a mdb is to avoid file corruption, improve multi-user
reliability, avoid file corruption, make maintenance easier, avoid file
corruption, improve working over the network, and avoiding file corruption.
Did I mention that it will make file corruption less likely too?

All the best

Tim F