Second answer:
I guess, some people didn't realize that you cannot boot the system if you
cannot go beyond the PROM Password. Someone suggested removing the PROM
and waiting 24 hours until it resets. However, since it is EEprom, that
won't work either. Another suggestion was to pull out the PROM when it
asks for the password and try to continue booting. This worked partway.
It aborted after reading the vmunix from the internal disk. This method,
I suppose, can be used to boot from CDROM or NET but I didn't try.
Here's what worked: I pulled out the PROM, opened up another Sparc5 that
was already running, and swapped the two PROMs. (Yes, this is risky, you
might blow something on the motherboard trying to plug things into a live
board.) After that, became root and used eeprom command to set
security-mode=none
Once again, thanks to all who replied.
Prasad Dharmasena <pkd@isr.umd.edu>