Give the wsmouse protocol a try (device is /dev/wsmouse0)
This works for me with the microsoft 2-btn ps/2 mouse. 

The first rule of Fight Club is: You Do Not Talk About Fight Club.

// Erik Huizing   huizing@cpsc.ucalgary.ca
// www.cpsc.ucalgary.ca/~huizing

On 9 Mar 2001 Matthias.Gack@gmx.de wrote:

> Hello,
> 
> I`ve got a PS/2-Mouse (Logitech wheel mouse) an want to use it with NetBSD 1.5.
> On writing a xf86config-file after installation follows "no such file or directory".
> I tried the protocols /dev/psaux (like in linux) and  /dev/pms0 , there was two times the same error.
> Who can help me ?
> 
> Thanks
> 
> Matthias  
> 
> 
>