There was an earlier version of hsfmodem without speed limitation distributed by Dell for Ubuntu Hardy. There are Ubuntu users who use it in conjunction with the current version of hsfmodem. They had to apply many patches.

I do not think that it is legal to use a driver from Dell without hardware sold by Dell. In my opinion the driver was for their customers only and not for anybody who does not want to support developers but use their products.

You could consider to buy a new modem for the serial port, but most modern computers only have USB ports. Thus most people would also have to buy an adaptor that converts the USB port into a serial port.

I think that your issue is solved because you can Knoppix V7.0.4 make work with your dial-up modem although you have to use additional software. It is not necessary to download the DVD version of Knoppix 7.0.4.