Ahh an SGI thread .. I like SGI's :-)
Your first port of call should be :
http://www.nekochan.net The Wiki is good, and the Forums even better, packed full of SGI nut cases :-)
NetBSD should go onto an Indigo2 quite well, Linux might go, OpenBSD is probably OK (but ran like treacle on my O2) but you best bet is still IRIX, in the link above you can find the Nekoware pages, it's lots and lots of opensource software compiled for IRIX .. you'll be looking at the MIP3 ports unless you upgrade to an R10000.
IRIX installation isn't to hard to install, just ask for help on Nekochan if you want help.
If you want to netboot your IRIX (because say you don't have a CDROM) you can use
http://zachrisson.net/DINAIf you want any help just ask, I've an SGI Fuel and and SGI O2 .. mmmm pretty hardware! ;-)
Regards
Mark
