There's a limit of 2GB on the size of an mdb file in Access 2000 (1 GB in Access 97) - not sure if this got upped again for Access XP.
Subject to this, there's no fixed limit on the number of records or the size of a table. If necessary you can store different tables in different mdbs; or you can use SQL Server Express (which i think has a 4GB limit) as the back end and store vastly more data than this.