IPSEC is the way to go (Score 1)

My previous job involved this stuff - you should look into IPSEC - We had some kit from TimeStep/NewBridge/Alcatel called "Permit/Gate". They have a Hardware box (2 port Ethernet VPN Encryption Gateway) and a WIN95/98/NT client too. Some of my customers use to use OpenBSD but as IPSEC is "opensource" you could [should?] interoperate *most* IPSEC implementations, and aparently KAME/FreeSwan have been involved in the Bakeoffs for testing IPSEC too (all vendors are suppose to do this for interoperability testing). A pure TimeStep solution works a treat but I knew someone who used their WIN client with their OpenBSD for example to get WIN clients into the network. Sounds like this might be the GO for you!