Question about this MDB file... Is it separated into a front-end and back-end database? If so, is it self-created or from a vendor?

I've had good success with using mysql as the backend database for MS Access apps. MySQL server will run on both windows and linux and is significantly more stable for a network environment than an Access mdb file. You then simply link the tables through odbc and you'll never know it's there.

If you were to run MySQL or some other database of your choice, you could remotely connect to it through an SSH tunnel as opposed to a full VPN.

I had a similar situation for our reps when on the road. We have a customer database with an access front-end and mysql back-end. I wrote a little script that detects whether they are on the local network or not and if not, opens a ssh tunnel with putty and starts the database and automatically relinks the tables. Works great for our needs.