Reporting back for the record in case anyone else runs into this problem
(and someone surely will if they follow the current PDF guide at
javahelp.dev.java.net
and use the now-defunct DTD URLs listed therein)...
I was able to get our nightly builds up and running again by downloading
the JavaHelp 2.05 latest release ZIP, installing its DTDs on the local file
system,
and replacing references to the v1.0 DTDs at the Sun URLs that just became
unavailable with a "file://" reference to the local DTDs instead. Your
mileage may very,
but our particular JavaHelp content, though developed for a v1.0 DTD,
wassuccessfully processed against the local v2.05 DTDs.
Glenn Picher / DeskNet