Genesis, There are plenty of pottential pack rafting trips in Tas. Some include, Dension, Franklin, Jane, Weld, Murchison, Davey/Crossing, Anne. All with varying difficulty levels, due to the remoteness I wouldnt recommend any to beginners, but would recommend day trips first to learn about paddling, day trips ive done in the learning process are Picton, Ringarooma, Meander and Leven.
http://www.paddletasmania.canoe.org.au/ ... Page=15629 is a good reference for Tas rivers.
As far as the Franklin goes, i wouldnt bother walking out via frenchmans but continue down to experience one of the states great rivers. Check out roman dials blog (http://packrafting.blogspot.com/) so much packrafting info on there including videos of the Franklin and Anne river.