Long story short, well, short as possible.

...already had a copy of SETopo map on my Garmin Nuvi's SD card. Works great (thanks, BTW)
Wanted a Wyoming Topo in there too. Re-read the tutorial...downloaded a copy (and installer) of the Wyoming Topo map. Successfully got the Wyo-Topo in Mapsource, cut and sent it to the Nuvi's SD card. Problem is that it seems to have uninstalled the older SEtopo map that was already there.
I seem to recall that you had to rename a newly loaded "gmapsupp" to keep this from happening, so I deleted the WyoTopo map, reinstalled the SEtopo. Then I left the SEtopo file name "gmapsupp" and dragged in the Wyotopo. Named the Wyoptopo "gmapsupp 2". When I go to see what the Nuvi is "seeing" in its maps setting. The only ones it can see is CN (which is already in internal memory) and SETopo. No Wyotop is an option. I can "see" the other WyoTopo from the PC's USB port.
Can y'all tell me what needs to be done. Thanks.