Hmm, a little more info on your setup might help. You mentioned you were running on a 486/celeron. Which is it and what other hardware , memory, hard disk etc.

You could try:apt-get clean and try re-installing. you might need to run: apt -get -f install. Alternatively you could try installing a newer version by specifying the branch from which to install:
Code:
apt-get -s -t unstable install aptitude
. The -s flag simulates what apt would do, you would run the command without it to actually perform the install.

You could consider upgrading all your packages to unstable, the reason being that since knoppix is a mixture of stable, unstable and testing versions of packages , subsequent upgrades usually lead to conflicts between versions, and upgrading or downgrading to a common branch can make things a little more manageable. However as those who warn against using knoppix as an debian installation source suggest, you might be better served by installing debian proper.

However it may be that the warnings of installing to HDD are starting to ring true.

hakix looks interesting, I'm not sure it will help as it seems to be geared towards etch.