>Right now we have some VB apps that use SQL 6.5 on the back end. We have about 20 active users. most of them doing simple inquires into inventory available for instance. I dont believe we have a busy system. The software seller tells me that SQL 6.5 is overkill.

IMO, SQL6.5 is too big for your purposes. Also note, that getting SQL-server (or other RDBMS back-end) you don't get speed advantages (in reality VFP will work faster), your gains will be in getting some frills like ready-to-use security, backup, replication etc.
PS: VFP works OK with SQL-server too, providing normal C/S apps