I tried this and several variations of it weeks ago, and the modem still was not detected by kppp (this is a hard-drive install). This is something of an oddball system (an Advantech shoebox-sized embedded PC), but RedHat Enterprise 3 and 4 are able to detect and use the modem just fine. Personally, I've given up on Knoppix/Debian for now, although we may want to get back to it some time.

If someone on the Knoppix team would like to try to get to the bottom of this we may be able to make a machine available on the network.