The odd person has asked about this subject in comp.os.solaris before so I'll
post my (partial) success for all who are interested.

I have successfully installed Solaris 2.7 on an SS5 using a linux machine as
the install server.  Unfortunately, I needed an Ultra running Solaris 2.6 for
one part of the procedure.  Perhaps someone can figure out how to do this
entirely with linux and let me know.

The machines I used:

  ss5box   - an SS5 with 1GB disk and 64MB RAM.  No operating system.
  linuxbox - intel RH5.2 with kernel 2.2.0pre4.  This machine has two network
             cards and acts as a firewall/router with ip masquerading.  The
             ss5box and linuxbox are on the same subnet.
  ultrabox - an Ultra2 running Solaris 2.6.  This machine is located on the
             internet about 5 hops away from the other two machines.

The software required on the linux machine includes:

  - rarp compiled in the kernel or loaded as a module
  - tftp and inetd configured to run it
  - nfs server and portmap
  - bootparamd

First, find out the ethernet address and pick an IP address for ss5box.  
Make sure ss5box is in the /etc/hosts file on linuxbox:  ss5box

Setup rarp:

  linuxbox# rarp -s ss5box 00:00:3b:80:43:79

If you wish to verify that rarp is working, run tcpdump on linuxbox while
attempting to boot ss5box:

  ok> boot net

Next, you need to figure out what kernel ss5box is going to attempt to load.
tcpdump can help with this.  My machine wanted C0A8850D.SUN4M.  To give it
this kernel, create the following symlink in /tftpboot on linuxbox:

  linuxbox# ln -s /cdrom/Solaris_2.7/Tools/Boot/usr/platform/sun4m/lib/fs/nfs/inetboot /tftpboot/C0A8850D.SUN4M
  linuxbox# ls -l /tftpboot
  total 1
  lrwxrwxrwx   1 root     root           68 Jan  5 22:48 C0A8850D.SUN4M -> /cdrom/Solaris_2.7/Tools/Boot/usr/platform/sun4m/lib/fs/nfs/inetboot

If your machine is not sun4m architecture, substitute your architecture in the
appropriate location above.  Also, it is assumed that you have the Solaris 2.7
installation media mounted at /cdrom on linuxbox.

If you now attempt to boot ss5box, it should indicate that it is loading the
kernel, but then fail with some RPC timeouts.  

To setup and run bootparamd, first create the file /etc/bootparams with the

  ss5box root=ultrabox:/tmp/sol7/Tools/Boot install=linuxbox:/cdrom boottype=:in root_opts=:rsize=8192 ns=

Run bootparamd on linuxbox with the command:

  linuxbox# rpc.bootparamd -d -r

This runs bootparamd in interactive mode with debug messages on.  Run this in
one xterm window. is the IP address of linuxbox on the interface
connected to ss5box.  

Two NFS servers are required.  One to serve a root filesystem to the install
program, and one to serve the installation media (the cdrom).  Unfortunately,
I was unable to get linuxbox to serve both of these purposes.  There seems
to be something wrong with having a linux machine serve the root filesystem.
The filesystem is successfully mounted, but the Solaris machine reports NFS
read errors.  To get around this problem, I used an existing Solaris machine
(ultrabox) as the NFS server for the root filesystem, but used linuxbox to
serve the installation cd.  

/etc/exports on linuxbox contains:

  /cdrom  ss5box(ro,no_root_squash)

/etc/dfs/dfstab on ultrabox contains:

  share -F nfs -o ro=linuxbox,root=linuxbox /tmp/sol7

It is interesting that ss5box has no trouble mounting the root filesystem
from ultrabox via IP masquerading.  The root filesystem on ultrabox is
copied from Solaris_2.7/Tools/Boot/ on the installation cd.  

These steps should be all that is required to install Solaris on ss5box.  
Start the installation process with:

  ok> boot net - install

A few error messages will appear, like 'no domain set' even though bootparams
does have a domain set.  Also, there will be some message about not having
access to jumpstart parameters.  Just hit [ENTER] to do an interactive
install.  The installation should be successful.  

I hope this helps people get Solaris installed on their SparcStation without
a cdrom drive.  If anyone figures out the problem with NFS, please let me