Sorry for replying to my own topic... A few things have come to mind.
I've seen this thread, which describes my situation, but that fix doesn't appear to be doing it:
viewtopic.php?p=1900&highlight=#1900
Also, I'm trying to install the 3.0.0.222 version of BullZip. I'm running from a full administrator account on the machine, and am in "install mode".
One more update: Here's the info that JR requested in the prior thread about similar issues, just in case it comes in handy here. It's a 32-bit server with the 32-bit version of Windows 2003 Server. I've got the 3/25/2007 2:03pm version of bzpdf.dll with file size of 192,512 and version 3.0.0.27.