You can use the Internet connection sharing if it is IP traffic. Setup your connection to dial where you want (doesn't have to be the Internet). Follow the instructions for Internet connection sharing except don't set the default gateway on the workstations to point to the server, leave it at its current value. Add a route on your real default gateway (if you have one) or on each workstation that points to the server for the remote network. i.e. if the remote network is 200.200.10.0 and your server is 192.168.1.10 then use the following:
on gateway (cisco):
ip route 200.200.10.0 255.255.255.0 192.168.1.10
-or-
on workstations:
route -p add 200.200.10.0 MASK 255.255.255.0 192.168.1.10
If your not using IP then there is software (winPort) being one that treats your server modem sort of like a shared printer. The workstation have a virtual modem that is mapped to the server modem. Works great.
HTH