I successfully configured my PCI based Rockwell/Conexant 56K internal modem on Red Hat 8. I downloaded an rpm for it from a website (sorry can't remember it but it came up in Google search front page). I think it was http://www.mbsi.ca/cnxtlindrv/
It was run by a single guy who had rpms for Athlon, Pentium, Celeron, PowerPC, etc.
Mostly the downloads were split into two distinct categories - HCF and HSF.
Originally, I downloaded the HSF (software) version which didn't work but on realising my mistake downloaded the HCF version which installed like a dream (simply double-click rpm icon) and the modem has run fine ever since.
Hope this helps.