I don't think you need to use a new kernel. As I read it, you can build speedtouch, download the firmware and it'll work just fine with the existing kernel.

Here we're just talking about the difference between internal and external kernel modules.

While there are good reasons for both approaches, generally it's easier to build an external one rather than compile a kernel (it's a much smaller download, for one thing! and you won't break anything else if it goes wrong).

I see that there are instructions for Sarge which -- used with caution -- should be OK for a HD install of Knoppix.