On Wed, Dec 19, 2001 at 01:07:13AM -0000, jwbirdsa@picarefy.com wrote:
> 
>    Nope, it's a straight install of 1.5.1 base/kernel/etc/misc. Take the
> same hard drive, plug it into a 486-based machine, and NetBSD is perfectly
> happy. Also, one of the 386es had a socket for upgrading to a 486, and when
> I plopped a 486/33 in and reset the jumpers, that machine came to life.
> 
>    I wish I had a 387 handy. It's beginning to sound like that's what makes
> the difference. Weird.

As Jared mentioned, it is a bug.  Boot a 1.5.2 kernel and see what you get.
From CHANGES-1.5.2:
sys/arch/i386/include/reg.h                     1.16

  Redefine register offsets using offsetof().  Fixes math emulation
  lossage.


-Andrew