it is actually possible to install debian from a system that has booted into
knoppix. check out
http://www.inittab.de/manuals/debootstrap.html
basically it allows you to install debian onto hardware that is detected by
knoppix during startup. i guess the only problem might be when finally
you have to boot again. The debian system will boot using the kernel that
was installed from debian, which might not recognise the hard drive.
i sudgest
http://www.backports.org/ where you can find a new kernel
for older debian releases.