Welcome to LQ.
Normally, if it is a
genuine hardware internal modem, then Linux will see it as extra serial ports. I have two onboard serial ports, so listing /dev/ttyS* shows /dev/ttyS0 and /dev/ttyS1. If I were to have an internal hardware modem, then it would show up as eiter /dev/ttyS2 (COM3) or /dev/ttyS3 (COM4). If you know which port it
should be on, then you could try specifing that when you run minicom or kppp.
Unfortunately, the majority of PCI modems (normal ones, not ham radio modems... that is what you're talking about?) are
software modems which rely on (Windows) drivers doing all the hardwork and not actually needing as many components on the PCB... and as such they're called WinModems. If this is where you think you're at, then check out
Linmodems.org and see if you can find your modem, and whether it's been OKd for use with Linux or not.
Good luck.