mouse flipping out

[J Patrick Draine]

Hi All,
While wading through the day's e-mail my mouse started to freak out -- 
scrolling all over my mail, making crazy repeated tones -- sounding 
like someone playing really fast trills on one note of a xylophone! It 
would stop I while hold the button down, start again when I let up on 
it. It also started "doing stuff" like turning IE on (from the Dock I 
suppose).
I'm writing this on my iBook -- it is the 500 MHz iMac (OS X 10.2.8) 
that's acting up.
It isn't the mouse itself -- I swapped a different one in and it 
behaves the same way.
Any thoughts?
Meanwhile 'm running DW3 and crossing my fingers.
Patrick