|Where to begin :-)|
Your users should not be in a different subnet than the server. One reason for this is you can only use one gateway. So if they have internet they can't access the server.
All workstations have to point to the servers ip for dns.
In turn you put your isp dns ips in the forwarders in DNS [not to be confused with forward lookup zone].
This way when a workstation makes a request for yahoo.com, your dns server forwards it to the isp who in tern returns the answer.
I was not aware you could install SBS without DNS. You certainly can't have AD without MS DNS on that server.
Answers are only as good as the information you provide.
How to properly post a question:
Sorry no tech support via PM's