I get a segmentation fault on V 3.4 while booting into the 2.6 kernel. I found the workaround to be to specify the noscsi cheatcode on the boot: line.

System details:
Shuttle MN31N motherboard with Nvidia MCP sound
Gigabyte Radeon 9200 video

Otherwise, a pretty generic system. Here's the boot line I used:
knoppix26 noscsi dma xmodule=radeon xvrefresh=85 screen=1024x768 lang=us

Since I had a free ReiserFS partition on my hd I also specified tohd=/dev/hda4 to copy the CD to the hd.

I must say Knoppix 3.4 is working beautifully!