No clue on the dual-boot issue, but...

Documentation I have on HD Installing Knoppix - Minimum Requirements:

Pentium-Class processor, preferably 300MHz +
64MB RAM
A spare partition on your disk, minimum 3GB
And the Knoppix CD

From my documentation - 3.GB is then broken down into Linux and Linux Swap:
Swap partition is recommended at minimum of 256MB
Linux partition is recommended at minimum of 2.5GB - don't know where 256MB went in their calculation

As far as the dual-boot though, I do know that Knoppix prefers to use LILO, and can be cantancurous if it isn't using it - maybe LILO can be setup to boot Knoppix and your other boot manager ( I don't know this one )

Cuddles