You’d have to use some kind of internet sharing software like proxy server or get a hardware solution such as LAN internet modem. You can’t just dial out to the internet ISP from a win 9x PC through the server. Using connection-sharing software, theserver dials out and controls the connection and the PCs will then access the internet via the one connection. The PCs have no control over the connection.
Depends what you want to accomplish. If you are looking for Internet Access, use MS Proxy server on your NT server (or on another dedicated server) to share your Internet connection (or another Firewall device for that matter).
If you want the workstations to actually dial-out for various reasons, you will need a modem sharing application. MS Small Business Server (SBS) has this feature/application built-in. Otherwise, there are many packages that will allow this. Most require a client app at the desktop to redirect com ports to the modem on the server. I have used the SBS and SpartaCom.