On several versions of kernel 2.6.x I have had a problem using the Synaptics Touchpad on my Dell Inspiron (5150) .

It moves the mouse in x and y as expected, but I cannot tap the pad to generate a mouse click. After googling around a bit, it seems that this is a known problem in 2.6 and while several fixes and workarounds are proposed, the one that seems most useable for Knoppix 3.4 (kernel 2.6.5) is to include the following as a "cheatcode" parameter to the kernel:

psmouse.proto=imps

such that your Knoppix 3.4 CD boot cmdline might look something like:

knoppix26 lang=us dma xmodule=vesa screen=1280x1024 psmouse.proto=imps

hope that helps
rgds,
Dave L.