....post fell through (think it was Galeon, not zIWETHEY).
'sparc boot disk' on Google turns up anything but Solaris refs, and the only Sun doc I found was for something like making your own boot CDROM tool.
Looks like, if you can't recover via STOP-A (and that was mentioned), the best bet is to try booting an alternative OS, NetBSD or Debian Linux would be my bets, and try to repair damage there and/or come up with a real Solaris boot disk. Note that there didn't seem to be much on the topic of creating bootable Solaris media, I don't know that it's possible. Free 'nix has Sun's ass kicked all over creation in this area.