Silicon grahpics O2 computer

I am new to this site. I have been hacking Dss and cable for some time and have worked on computers for years.
I just got my hands on this Silicon Graphics O2 computer running irix 6.3.
I need this O/S to restore the system. Every thing is locked up via a admin password, I don't know the pass word.I would like to bring the system back to out of box, or maybe install a different O/S.
Does anyone have any background with this computer??
Thanks for any help you guys can give.

LG