For anyone who cares, the 'correct' username and password for the Underscore Hosting site are
Unfortunately this information is entirely useless, as my IP isn't acceptable.
New working theory: doing some portscans, it appears that some of these sites have telnet/ssh enabled. Perhaps with appropriate credentials, such as those of the elusive Beth, we might obtain shell access to a machine that does have an acceptable IP, and might then use telnet or lynx from there to retrieve useful information?
I'm wondering if there actually is a puzzle here. It seems inconceivable that someone would dig a rabbit hole quite this deep...