I've tried a number of combinations of the opms, pms, and pmsi driver (yes, 
only one in the kernel at a time) and I've tried using /dev/wsmouse0 and 
/dev/pms0 as the pointer device in the XF86Config file.

The only arrangement that has worked was opms /w/ /dev/pms0 and pms /w/ 
/dev/wsmouse0.

How can I enable my Intellimouse so that I at least get to use it as a 
three button mouse?

I'm using NetBSD-1.4.1