I had this problem in Xubuntu 6.06 LTS (XFCE) on an old AMD K6-2/500 with SiS 530/5595 chipset. Very difficult to login at the login window. Add the kernel parameter 'clock=tsc' in GRUB (ie: to the 'kernel' line of the top kernel entry in /boot/grub/menu.lst). -- Erratic keyboard repeat https://launchpad.net/bugs/55843