Did you try putting the drivers for your mouse in the extensions folder in the OS 9.1 System Folder?
I haven't tried it myself (I boot back into 9.1 to game), but I would give it a shot. If you haven't tried the USB Overdrive extensions instead of your manufacturers drivers, check them out too. I abandoned Kensington Mouseworks after trying them on for size. You lose chording, but that's about all. Oh, you won't crash as often either.