>>....this time Knoppix tells me something wrong with CUPS.

Any more detailed error message?

>>...56K modem.

This is almost certainly a winmodem. I have got winmodems to work using ltmodem (see
http://www.knoppix.net/forum/viewtopic.php?t=12119 & http://www.knoppix.net/forum/viewtopic.php?t=12909) but I'm not sure if it can be done with a PMI since installing ltmodem involves installing an application which can normally only be done through klik when using a PMI.