I have run all the necessary debugging, getting io space permissions as 
user root with i386_get_ioperm and then reading and writing io space 
using inb, outb, inw, outw yields the following:

- the ioperm read map is initially always all 1's
- setting 0's in the map at addresses where I wish to write always 
works, even if the addresses are taken by a configured driver (setting 
zeros according to the manual page)
- reading from any address works
- writing to any address always busfaults, regardless of whether the 
address is owned by a driver or not

Kernel is netbsd-1.6.1 GENERIC, /dev/io is not configured

I conclude that what I am trying to do is not possible (can't write to 
kernel io bus space) with the current kernel.

any comments are welcome, thanks,
Peter