You can use different kernels but you must have kernel specific cloop.ko and unionfs.ko files, too. You can do it in a very simple way.

Just make so many modules directories with different names under /KNOPPIX, e.g. /KNOPPIX/modules_402 and /KNOPPIX/modules_501. Then place corresponding modules under those directories.

Then you must tell to the kernel where these modules can be found. You must modify linuxrc file. This is what you have in Knoppix 5.0.1:
Code:
MODULE_DIRS="/cdrom/KNOPPIX/modules /cdrom2/KNOPPIX/modules /modules /modules/scsi"
Change the directory to the same name where your modules dwell, e.g.:
Code:
MODULE_DIRS="/cdrom/KNOPPIX/modules_402 /cdrom2/KNOPPIX/modules_402 /modules /modules/scsi"
Was this what you were asking? But if you really want to have two different /KNOPPIX images (e.g. /KNOPPIX1 and /KNOPPIX2) to hold different Knoppix versions, I don't know if this is enough. I have always used one compressed /KNOPPIX image and have never tried your idea. And believe it or not, my image is about 3 Gt (no 2 gig limit existing any more with new Debian programs).

-tapsa-