random mouse?

[Simon Gerraty <sjg%juniper.net@localhost>]

On a dell gx620 running 

NetBSD chaos 5.1_RC1 NetBSD 5.1_RC1 (GENERIC) #0: Sun Apr 25 06:21:36 UTC 2010  
builds%b7.netbsd.org@localhost:/home/builds/ab/netbsd-5/amd64/201004250000Z-obj/home/builds/ab/netbsd-5/src/sys/arch/amd64/compile/GENERIC
 amd64

USB mouse and keyboard.

The mouse is driving me nuts - moves almost randomly.
Sometimes the pointer moves at 90-180 degrees from the direction the
mouse is moved.

I've tried a couple of different mice, including a ps2 one via a usb
adapter.  

Thoughts?