I have no real experience with Knoppix but considering that it is based on Debian you should probably also consider wiping it out of your system and doing a fresh Debian install. Do a network install of the stable idepci version, and then upgrade to SID. That is the version that has worked for me: with just two floppies it downloads and installs the whole system, following the simple instructions. Full details at the Debian site, under "network install".

That does seem like the best option but I'm on dial-up and I've already spent so much time downloading one thing after another to get a linux system and I'm just not prepared to spend yet more time downloading such large files, especially since my 2.4 kernel works fine apart from the odd crash and Windows XP works like an absolute dream so I don't think I desparately need to get a 2.6 kernel.
Just something I wanted to try but it can wait a while. I'll maybe try when I go on broadband (a month or so).
I'm wondering if I should wipe out the Knoppix-Debian install and try Gentoo which I have on disk.
I tried it before Knoppix and I gave up because I couldn't get my modem to install but I may have more luck now.

For gentoo you really want a broad band connection, get slackware, its the oldest standing linux distro, though not the most user friendly ... but if Gentoo doesn't worry you, and you have debian experience, Slackware should be easy.

Still ... it is odd.

Yeah, Slackware was one of distros I was looking into before I chose Knoppix so I may have a go at that.
I dunno though cos once I got the modem sorted out I haven't really had any major problems with Knoppix-Debian til I came to try this 2.6 kernel, which I'm still not sure I actually need.
Incidentally, I can't remember what I actually did but I got make xconfig to work again and I tried building this 2.6 kernel yet again and this time tried ernobe's suggestion of using the same append options as the 2.4 kernel but I'm still getting the same problem.

Ok, it's been a couple of days but I now have the new 2.6 kernel installed and it's booting fine and everything seems to working except for one thing - my modem.
The modem is an Intel 536ep Data Fax Modem and once found the right driver this installed fine with the 2.4 kernel but for some reason I can't get it to install with the 2.6. ./configure goes fine but when make 536 I get lots of scrolling text for a while but then it stops with a message that the kernel version is 2.6.8 though there are no other error messages at all. I have tried 6 different 536ep drivers including one that said it was specifically for 2.6 kernel. Could anyone point me in the right direction?