Walkingirl and ukmuse, I agree with Mike, if you are considering the TGO challenge as a long distance walk then go for it, but beware!!!...it kinda gets under your skin and makes you want to return the following year for more. I have just completed my third Challenge in as many years and no doubt I'll be back next year for another crack at it.
It is a totally unique event in that you plan your own route, which is part of the enjoyment, and there are so many options. You can plan the route to suit your requirements, be it high level taking in Munro's or low level through some wonderful Glens. There is also a lively social side to it too (if you want it) with many get togethers along the way.
As a starting point for your planning I recommend the book"Scottish Hill Tracks" which details many long distance routes on tracks and rights of way through the Highlands.
I would post some photo's to whet your appetite further but I can't work out how to do it.