OK, I too have included an updated 2.6.22 kernel to my remastered ISO and..... it doesn't work (still loads but uses kernel 2.6.19).
I've dug a little more deeply and believe I have the answer.

I'm remastering using the wiki process, so boot from a live cd, expand the contents of the cd to a free partition create source and master, work on the cloop, make changes, create a cloop again and then an iso.

The contents of the /cdrom/boot/isolinux are the answer.

These are isolinux and boot directories are copied in the master location, it is the file isolinux.cfg that controls the boot process.
AFAICT this file contains links to the booting process (default) boots the standard kernel expert includes alternate options.

To use your new kernel back up the file called linux in the /boot/isolinux folder and place your kernel here.
The initial ramdisk, there is a file called minirt.gz when I expanded this it looks as though it might be an initrd, but then reading through the knoppix
wiki this is a compressed ext2 filesystem.

I have not yet tried this myself, but one way around this is to compile a kernel with support for your root filesystem and any other devices that need
starting at boot time e.g. scsi drivers.
Its not an acceptable solution if you want to try out different hardware but may work. I will post back in a few days if I get this to work myself.

Books, I've searched on Amazon and found knoppix hacks (I've ordered it for myself) and the reviews look pretty good.