Mouse keeps freezing every few seconds, why?

I just downloaded 5.1.1, and it has the same problem I saw in the 4.X releases.

The mouse keeps freezing periodically -- perhaps every five seconds, for about a second each time.

My hardware: Asus Terminator (A7VT) with Sempron 2800+
Mouse: Microsoft Intellimouse with wheel and LED, plugged in via USB
(the mouse has a USB-to-PS2 adapter as well, but it burned out a few months ago).

At this point, I am still using Knoppix 3.7, because that is the most recent release I can find which doesn't have either this mouse-freezing problem or the weird new filesystem for USB-flash drives (which tended to go splat and lock the machine up for several minutes, and sometimes caused data loss). I first noticed the mouse freezing in 4.1 when I tried that (never saw 4.0).

Any ideas? Thanks!