Different databases

I have a program that uses an Access database (old.mdb). I am in the process
of updating the program and wish to use a similar but enhanced database
(new.mdb) that shares many of the old fields. My question is what is the
best way to differentiate one database from the other ? The old program is
written in VB6, the new is in C#. If an old database is recognized, I plan
to convert the data to the new database. Is this the best plan ?
I am not looking for specific code but would like to find out the best
methods.
Thanks in advance for your help,
Jim