This isn't going to be easy, or supported. The problem is Microsoft -- there is no MS provided (and thus supported) JDBC driver for Access. You can use the JDBC-ODBC bridge from Sun to connect to Access through ODBC, but you can't make a WAS datasource on the JDBC-ODBC bridge.
You could buy a 3rd party Type-III MS Access JDBC driver (for instance from these guys) and try creating a datasource on that, though. This would use the generic datasource support from WAS -- similar to what is in this articleabout MySQL. To a great extent, though, you're on your own in getting this to work.