> What does "we don't support" mean? isn't it working at all?

I'll attempt to clarify, as it were. The LG1 isn't supported. The fact
that you're using a VGA monitor may or may not be relevant; if your
Indigo has an hd15 ("VGA") connector, it's an LG1. (I bring this up
only because I've used VGA monitors with non-LG1 graphics cards, but
then I have this bin of funky adaptor cables...)

> What kind of output should I see via PROM routines? I don't understand
> really well...

You'd get a plain textport, which is white text on a purple background,
drawn by the PROM as it emulates a dumb terminal. In other words, you
can't run X on the LG1 without IRIX, proprietary undocumented blah blah blah.
This goes double for the dual-head LG1 board, and that pun means I'm up
way past my bedtime.