I too run Knoppix on an older system with a 10 year old video card. Knoppix will only boot up with the "knoppix vga=normal" cheat code.

I installed Knoppix to the hard drive, it is the only OS on this PC, and I love it. It is the only distro that I have been able to get to work on this PC. Debain, which is very similar, Ubuntu, and Mandriva all hang a few minutes after booting up. I have no idea why this is (maybe it's because it uses KDE instead of gnome). If it hadn't been for Knoppix, I would have given up on linux a long time ago.

If you do a hard drive install, you will have an opportunity to specify some of the settings, so you can probably select less demanding display properties. It was a few months ago now, but my hdd install was a snap. Been running fine ever since.