1: is this possible ?
Absolutely. Just remember that your hard drives will be hda, hdb and so on. The hda will be the primary master. You'll just need to point the installation at that.

2: If it is, how do I go about installing knoppix to the 4gig drive
Depends on which installer you use. There's a link to at least the old install method here:

http://www.knoppix.net/docs/index.php/HdInstallHowTo

Make something like 300Mb as a swap partition (linux swap) and the / partition ext3.

3: do i need to prepare that drive in anyway before hand ?
Nope. The install calls all the tools necessary.


4: Is 4gig enough for knoppix and any other files i create/add (baring in mind im still learning/experimenting with linux, so i wont be making alot of extra files)

It should be: you can remove substantial parts of the Knoppix install anyway to make more space.

5: is there anything else i need to know before embarking on this mission?
I'd advise that as soon as you get up and running you do (as root)

apt-get update

then

apt-get install synaptic

then (still as root) use synaptic to download the HOWTOs and maybe both the rutebook and linux cookbook.

Have fun!