well i'm finally making some progress.  installing NetBSD now as we speak.
from what i can make out, the ROM on the 5000/240 and the tftp server that
SUN Solaris 8 (and possibly 7, but that's another story) are not compatable
at all.  i rebuilt my FreeBSD box, and netbooted the kernel from that thing
without a problem.  the Solaris 8 tftp server problem might be something
that should be documented.  it just doesn't work, and i doubt it ever will.
it seems like sun dropped some older protocol items that the 5000/240 still
needs to successfully tftp a kernel.  sad really.

i'll write later with more info as i find it out (as well as with some
questions i'm sure)

-brian

ps: i put a copy of the Solaris 7 tftp server on my SUN (running 8) but
unlike the 8 tftp server which complained about Protocol not supported,
this one just failed silently.  so it looks like a no-go for netbooting
these boxes from modern versions of Solaris.