solution found!

to install stuff that has to compile to kernel source then install another kernel source and header files using apt-get (or indirectly using kpackage for GUI) and do the job in the other kernel then come back to your knoppix kernel for correct hardware detection. for me, i installed kernel headers 2.6.11-1 whereas knoppix ships with 2.6.11. i also installed kernel image 2.6.11-1 and booted to 2.6.11-1 and successfully installed vendor-supplied video card driver, which required header files (2.6.11 don't have header files as deb package). then i was surprised to find that in 2.6.11 video card was succssfully configured!

another note: i discovered a very good program for configuring rt2500. use apt-get to install RaConfig2500 by installing package called rt2500 and other depended packages (should be automatic if you set up apt-get correctly using net connection as source).

happy knoppixing!