I'm not an expert, but I always have a working modem. and I want to help, since I get so much good assistance from this forum. It sounds like your login process is failing. Make sure you are doing what your isp requires. Find out if you need to enter your nameservers or if they provide them at login. Most likely you'll need to enable dhcp, unless you have a static ip address. Usually, setting dhcp and pap login works. Nameservers are usually provided at login. If that doesn't work, you'll need to check with your isp to find out how they negotiate the connection.
I think these settings are most straightforward using the "Internet Connection Wizard" in the K menu under system tools in RH9. Once it is configured correctly, the easiest way to bring up the connection is at the command line:
If more detail is needed let me know.