Mike,

I have the Supermicro Dual Pentium Pro (DNF) motherboard
that you mentioned.  It's working great!  I did not install
NetBSD on my new machine but Linux, FreeBSD, and OS/2 Warp.
The hardware configuration is as the follow:
    1. Supermicro DNF motherboard (dual pentium) 1 200 Mhz CPU
    2. 32 Mbyte 60ns EDO.
    3. Adaptec 2940UW (OEM for Supermicro) 
    4. Metrox graphic card.

You may want to buy the DNE model of the motherboard; it's
newer and it's a BABY size.  DNF is a FULL size motherboard
.  The only advantage for DNF is that you can fit any full
length add-on card to it without any problem.

good luck.

shao