I'm trying to install my sun 3/260 via NFS also. This is what I
understand of it:

The client looks for a file D0D62D05 (the IP adres of the client machine
in hex) on the server in the tftp directory. This file should be linked
to the netboot program of netbsd.

This program then loads the netbsd_rd kernel (I had to call it netbsd to
get it working) via NFS.

Then answer the questions root device etc. with the standard values:
md0, md1, ffs.

Now the install program starts (this is where you get the FPU error).

With the install prompt you can configure your disks (with edlabel) then
initialise the le0 (with ifconfig), and mount the server directory where
the miniroot exists via NFS.

Now copy the miniroot to the swap partition (/dev/rsd0b) of your disk
(with dd) and reboot the machine from the swap partition (b sd(0,0,1)
-s).

I never got this far because I get a 'device not configured' error when
I try edlabel or dd on /dev/rsd0c or /dev/rsd0b.

Why you have problems with your FPU I don't know.

Hope this helps a little bit.
-- 
Grtz Dimitri