Use the highest JET version.
DAO 3.5x can access a JET 3, and lower, mdb
DAO 3.6 can access a JET 4, and lower, mdb
For ADO there is an (old) provider for JET 3.51, and one for JET 4.
So, if you use DAO, then use v. 3.6
If you use ADO, use the JET 4.0 provider.
If you haven't done so, then upgrade to VB6 SP5 so that DAO 3.6 and the JET 4.0 provider for ADO are available on your system (SP4 makes them available as well, but upgrade to SP5 in any case).