Thanks for the respons Aay...

The CDs are fine (I have three) and I've tried toram and ide2=0x180 nopcmcia and still no go... here is what it says:
Welcome to the Knoppix live Linux on CD!

Can't find Knoppix file system, sorry. Dropping you to a very limited shell.
I suspect it has something to do with Dell's BIOS (I think I've read something related to it but I can;t remember where).

I wonder if there is a specific boot option to get around the problem.