I have a G4/733. (768 MB RAM, original superdrive, 10 GB HDD (OS 9.2.2), 120 GB HDD (OS 10.4.11), NVIDIA GeForce2 MX 32MB, 17" Samsung SyncMaster 730B, USB Apple keyboard (dated 1999), an Apple Pro mouse, and a Microsoft Comfort Optical Mouse 3000). I have had both mice connected to the keyboard USB ports with no ill effects. In fact, both work at the same time. I could, if I so desired, take a two-handed approach to my mac (interesting thought ...).

I have not seen the behavior you describe with either OS.

Have you tried an exorcism?

--David