Windows XP: scrolling, jumping, dancing, possessed mouse

scrolling, jumping, dancing, possessed mouse

I'm having some odd behavior with my mouse... I have Logitech G7 and MS Natural Kbd. on XP Pro.

What is happening, not all the time, but 3 or 4 times in the last week. If I'm typing, the cursor will scroll left and to the top of the page, line by line. When I use the menu controls in an application, whatever demon possesses control of my computer will cycle through the menus file, edit, view etc, not stopping on anything, mouse not obeying any commands.

Other oddities, if I reposition a popup window, the window will stutter and shake as if hit by an earthquake.

When shutting the computer down (tired of the demonic possession, calling it a night) the focus on the "do you really want to shut down" jumps between yes and no, allowing no clicks to be made. (I've never known this computer to be indecisive, just the operator).

So naturally I ran every virus scan available to me, Trend, then ran AdAware, then SpyBot. All were previously installed and reported nothing out of the ordinary (it wouldn't be that easy).

So what could it be? Restarting the computer snaps it out of whatever hiccup it was in, but then after a while it degrades into this degenerate behavior.

What next?