Access is multi-user enabled right out of the box.
The recommended approach is to split your application into a front-end
(containing the queries, forms, reports, macros and modules), linked to a
back-end (containing the tables and relationships). Only the back-end should
be on the server: each user should have his/her own copy of the front-end,
ideally on his/her hard drive.
Tony Toews has an introduction to the topic at
Doug Steele, Microsoft Access MVP
(no e-mails, please!)