I have not run into this, but perhaps posting a little more about your machine might help.
What chipset are you running on the mb?
what else is hooked up inside and outside of the box, hard drive, I'm assuming that is a USB keyboard?
There may not be enough of a user group here to diagnose a problem that specific (could be wrong). I see http://ubuntuforums.org
recommended a lot. Since this project is so closely related to Ubuntu itself, that might be another place to try.