I utterly refuse to quote ten levels deep... hurts my head I would think the best bet for running two ps2 mice with different protocols simultaneously would be gpm - you can configure (with a little trouble) X to work happily alongside gpm, and gpm allows you to specify protocol and has a -m (I believe it's -m) option to specify other mice.
Still, I think it might be a big 'ol headache - might be easier to convince one of the ps2 mice to talk the others language, through a series of hooked on phonics training and hardware gutting :P -Martin N. ----- This email has been sent as a single line of query, and in no way indicates the senders interest in or acceptance of any promotions or "opt-in"'s unless otherwise EXPRESSLY noted.