Wanted to bump this old thread with something I just learned.... Apparently ArcGIS now owns the old National Geographic TOPO! maps
http://www.arcgis.com/home/item.html?id=99cd5fbd98934028802b4f797c4b1732
Click on "open in map viewer" and zoom way in to see the map, or use one of the "famous locations" links on that page, such as
http://www.arcgis.com/home/webmap/viewer.html?webmap=931d892ac7a843d7ba29d085e0433465¢...9,40.689601&level=14
You can also download them with Mobile Atlas Creator and make maps that can be used on your phone, computer or dedicated GPS. I won't go into the details unless there's interest, but it's not too hard. Mobile Atlas Creator is a free open source program for Windows, Macintosh and Linux.
http://mobac.sourceforge.net
Anyway, this is one way to access the old National Geographic Maps without struggling with old software. And it's free.