I have a dual boot NT / Knoppix on a Toshiba laptop that has no CD drive and no floppy. I have an external PCMCIA CD drive, but to my knowledge, there is no way to boot knoppix off it, because it hangs very early in the process.

Here's how I got it working

2 partitions:
First is NTFS w/ WinXP
Second is FAT w/ Knoppix

MBR has the NTLDR bootloader.

I put w32grub in a separate directory on the NTFS drive. I set up boot.ini so NTLDR gives me the option of booting to WinXP or going to GRUB.

If I select GRUB, I have it pointing to the knoppix install on the FAT partition. To get this to work, I had to go to a second machine, make a boot floppy, and then copy the boot floppy files (vmlinuz and miniroot.gz) to the FAT partition via a network connection. GRUB uses those files to boot knoppix.

So now I can boot whatever I want without a floopy or CD.

w32grub is available at: http://www.skyjammer.com/files/knoppix/