Networks

Yes, but you are restricted to only one Domain Controller as SBS will not allow multiple DCs, you need Windows 2003 Standard or better for that.

What are you using the 2nd SBS server for?

You wont be able to run two DC's with SBS but you can have both servers running, especially since the VPN is mapped through the routers and not through the servers. I am getting ready to setup two sbs using the servers for vpn instead of the routers they currently have. Proper trusts and delegation are needed for the network to run right in either case, but it really all depends on what services you are running and what priorities are of greatest concern. But two answer your question, yes it is entirely possible although most would want to use standard edition or enterprise.