I'm having the same problem on a Dell Inspiron 4100 laptop. The keyboard works fine at the boot menu on the livecd but once I'm at the login screen it is no longer working. Went through my bios and couldn't find anything relevant. Does work with OS I'm about to replace. Also noticed that touchpad does not work either. Trying to acquire an external keyboard to see if that will work.
Plugging in PS/2 keyboard did not work either
USB mouse works however. Don't have a USB keyboard at the moment but I will try to get and and post my results.
USB keyboard worked. Installed PCLinux. Keyboard and touchpad on laptop still do not work once I get to login screen on fully installed system.