Since mdb format is very sensitive to network quality, I found it better to use a mdb file through a network mapped drive. So, in order to connect to a mdb file from the Internet, a vpn access is required. A few vba function were added to my apps to connect vpn and link odbc.
What I'm doing since for the last few months is to use a msql database through ODBC connection with an Access frontend. The results are surprisignly good for response time and I'm going this way from now on.
On a LAN, I just make sure a user starts Windows with a username known to the serveur (same username and password for windows and for server). The user is then made member of a group and that group "owns" an ibay with no internet access. The ibay is mapped to a letter and the mdb files are put in ibays\files.
Hope my experiences could help...