If you are talking about a DIAL-UP MODEM, use SuSE IGUANA -> INTERNET -> KPPP (Point-to-Point-Protocol) and follow the set up a for dial-up session.
If you are talking about a Cable MODEM, your SuSE system is ready, just plug in the NETWORK cable from your Cable MODEM to your NIC.
I have notice that some Linux distributions do not like USB devices (NIC, MODEM, Scanner), and might have interrupt conflicts. Try unplugging any USB device and test your dial-up/network connection again. If everything works, plug in the USB devices again until something does not work so you can find the problem device.