Okay, I think I've found the problem. Opcenum.exe is installed in the "C:\Windows\SysWOW64" directory and the path is not known to Win 7 when I try to run opcenum /regserver, so I have to instead include the path in the run instruction: C:\Windows\SysWOW64\opcenum /regserver.
I had also un-installed and re-installed with UAC set to minimum (turned off, basically), but nothing changed.
Here is the answer to one of my questions, straight from the UniOPCHelp: UniOPCServer installationAlthough OPC servers can be installed by any user having administrator privileges, we recommend that installation be done under local administrator log-on. In compliance with the OPC DA v2.x specifications, it is recommended to use the OPCEnum application, which enables OPC clients to browse the available OPC servers. This application is installed together with UniOPC Server.
So, clearly opcenum.exe is supposed to be installed by UniOPC. It looks like it was just installed in a location unknown to Win 7.
Elaborating on my symptoms...
From the UniOPC Help, I run into what may or may not be a problem here:
"11. Click the Default Protocols tab. The default protocols should appear as shown in the figure below; if they do not, update them."
Help shows two entries at this point: "Connection-oriented TCP/IP" and "Connection-oriented SPX". I have the first entry, but not the SPX protocol, so no, my default protocols do not match what the help information says they should match. Is this a concern?
I also have problems at this step from Help: Register OpcEnum: "Start> Run>OPCENUM /regserver". My 64-bit Win 7 PC says "Windows cannot find 'opcenum...'.
The failure in this step of the procedure caused failure in the next step, too, and OPCenum did not appear in the list of DCOM Component Services. After running opcenum /regserver with full path specified, OPCenum DOES appear in the DCOM list.
Not completely up and running yet, but got past the first hurdles...