Tinderbox vs Inspriration
I haven't used Inspiration but once so I'm not the best person to explain the differences. But, I would suggest downloading Tinderbox and the GTD file, then just start fiddling around with it. The outliner portion is pretty similar to Inspiration in some ways, but the map view is quite a bit different.
The best comparison between these two programs and many other outliners can be found at ATPO:
http://www.atpm.com/10.10/atpo.shtml
and
http://www.atpm.com/Back/atpo.shtml
One aspect of Tinderbox that is different is that you can have multiple views of the same set of notes: outline, explorer, map, and a few others I almost never use. [Important terminology: in Inspriration, Tinderbox's notes are line entries in an outline or the boxes in Inspirations map view. In Tinderbox, notes can contain other notes, which is another way of saying that one level of the outline (a note) can have other levels (notes) indented underneath it.]
Another difference is that you can also view them as text or html export files. This is where Tinderbox begins to be more complicated and requires some knowledge of html page construction (not a lot but enough to look at some references online, the Tinderbox Users Guide, the wiki, and just taking apart one or two templates by other Tinderbox users). But, once you figure out how to export and/or print your Tinderbox files, you don't need to mess with the templates for these much at all. In other words, the challenge and fun and power of Tinderbox is that you can customize it so much.
Finally, another difference is that Tinderbox doesn't force you to rely so much on just an outline or map view of all your notes. Because these agents (which are like other notes
I have a few screen shots of my GTD file that I could email you in case they would help. The first shows just the three outline views I use (full in Explorer view, an outline of the NextAction notes which is a collection of notes gathered by little agents which are little search criteria, and the InBox note). The second shows the two map views I use (one for project notes and the other for actions). The map view boxes are just notes with their titles and in the color I've set for each. This is just a convenient way to see lots of projects grouped (the background colors aren't notes but are "adornments" boxes that decorate part of the map view). It also is an easy way to move notes from my InBox to another part of my GTD "outline" without scrolling a lot. My screen at work is wider, so I have these windows off to the right when I'm working (not overlapping so much as they are in these screen dumps).