Have a look at this site

http://www.mbsi.ca/cnxtlindrv/index.html

theres a lot of information there. From what I understand there are two types of chipsets that conexant make, one is a controllerless one and the other is software driven. The site has a program that you can download and run to identify what sort of modem you have and download the appropriate set of drivers.

From what I understand there are good linux drivers for conexant modems, there just a bit fiddly more than anything.

By the way if it's an ADSL modem, this page is a good guide:

http://www.wlug.org.nz/AccessRunnerADSLModem

Hope this is of some help