I have not used MS Access myself (fortunately) but I believe it works much like the old, old way of achieving a multi-user database in FileMaker.
That is, it is not a true client-server database but more a peer-to-peer database and that each peer opens the same database file which is available to multiple user via file sharing. Therefore as elikness said it should just be a matter of putting the files on your Lion Server and then sharing that folder/volume using SMB sharing.
However one thing to be aware of, since MS Access is not a true client-server database I would imagine it uses record locking to manage simultaneous direct access to records in the same files. File or Record locking is something that has historically been a bit flakey when using Windows clients with a Mac file server (and probably vice versa).
While I am not proposing it as a solution to consider seriously, it is worth you knowing that FileMaker Pro is a database system that is available for both Mac and Windows and depending on how you configure things can be considered to stretch from a configuration very similar to MS Access at the low end all the way to a high-end MS SQL Server style setup at the top end. See http://www.filemaker.com for details.
There is also a a third-party tool available for migrating databases to or from FileMaker Pro and it can convert MS Access databases to FileMaker Pro see http://www.fmpromigrator.com/
You could use FileMaker Pro just on Windows machines if you wish.