There is a bug in the 2.6 kernel that causes the mouse to go erratic if you are using a KVM switch. Booting up without switching is just fine - its just that the mouse goes crazy if you switch back and forth between boxes. I have been trawling the net for answers, workarounds. Here's a few:

Use PS/2 to USB adapter for your 2.6 box
Knoppix 3.3 works with KVM switchers
Unplug the mouse cable on the switch and plug it back in

Add this to your kernel cmdline in grub or lilo
psmouse.proto=bare
You will lose your scrollwheel, but at least the mouse wont be erratic.


It appears to have been fixed in the 2.6.11 kernel
2.6.11 changelog

Input: psmouse - reset mouse before doing intellimouse/explorer
probes in case it got confused by earlier probes; switch
to streaming mode before setting scale and resolution,
otherwise some KVMs get confused.
Patch-by: Marko Macek
Signed-off-by: Dmitry Torokhov