I've been having the same problem here, and this cheat code works for me as well. Dell Inspiron 5150 with Geforce FX gfx;
knoppix nosmp
boots perfectly.

I've experimented with different BIOSes to see what happens; I tried the 02-16 and 02-09 versions of Knoppix, with BIOS versions A31 (latest), A29 (previous) and A26. All booted perfectly with the nosmp cheatcode.

No idea what I did to get this working, but it does, so I'm happy - don't have to wait for 3.4 to come out