If you've got something with a PC/MS switch, try changing the
	aux/mouse 0 and aux/mouse $mouseport
in /bin/termrc to aux/mouse -dC 0 ($mouseport)
and it should work with the switch in one position or the other.
Unfortunately, I can't remember whether the letters mean
PC vs Mouse Systems or PC vs Microsoft, so you'll need to try the switch both ways.
On those mice, only the Mouse Systems protocol supports 3 buttons.
I think that's right but it has been ages since I used a serial mouse
and I'm not at the office so I can't check the setting on the old mouse
I've got in a cupboard.

Dixons was selling 3-button Logitech pilot mice for a tenner recently
with PS/2-serial adapters.