> I found 3 NetBSD 1.6 ports for Arm32.

Only three?  Keep looking, there's at least 6 based on arm32 ;-)

> Which one should I use for my old Psion Series5 (non MX)?
> Is the 1.6 version compatible with my Series5?
> 

None of them currently support this platform.  But perhaps the closest is 
hpcarm.

> I need infos about this machine: where can I found them?

Sadly Psion have always been a little reluctant to publish details of the 
chips in their machines.  Some information is available, though I wouldn't 
be sure where to point you directly.

R.