if i figure it out.. i'll let you know. im having the same problem (G3 B&W Rev B, 10.3.6, 768MB RAM, 6G HD-OSX, 376GB RAID, ZIP, canon printer, Airport Express).
what are you running?
peace.
*im not able to reset PRAM on boot. i have yet to try any disk utilities.
I hope this information will help somebody who has this problem. I had this problem when attaching external USB keyboard. Once the keyboard was detached, the problem was gone.