Why don't just use XDMCP using a free X-Window server under Windows?
I use a nice one called Xming, thought it isn't developed any longer, it runs very well and is really easy to install and use.
When establishing an XDMCP session, if the screen stays black, it means that the XDMCP server (on IRIX, it's xdm) isn't responding, probably because of a misconfiguration. I don't know how to configure it, mine was working out of the box when I got my Octane.