In reply to PaddyMcQ:
Drop down into Glen feshie and make your way to Kingussie/ Newtonmore through the forest paths (have a look at the Scottish national trail route for this section) and either do East highland way or Corrieairyack to fort Augustus and down the great glen way
or drop down into Glen Feshie and use bridge or ford the river and work your way over to Glen Tromie via the path that leaves Feshie on the shoulder of Carn dearg Mor, walk west through Glen Tromie to Bhran cottage and then up via the Alt na fannich (you might have to make your own track here) and onwards to Loch Cuaich then onwards to Dalwhinnie.
From there its a glorious 40 mile walk down loch Etricht, culra, Bealach Dubh, Loch Ossian, Loch trieg, Glen nevis and Fort William
Have a look at this link to give you an idea of the land after Dalwhinnie
http://www.walkhighlands.co.uk/Forum/viewtopic.php?f=25&t=49099
Post edited at 15:20