The Foothills Trail is a work in progress that will eventually go from Sumner to Carbanado (up by the Carbon River entrance to Mt. Rainier National Park.) Here is a link to the foothills trail website. At this point they only have something like 15 miles paved and it doesn't connect with the Interurban trail yet.
here's an article in the Tacoma News Tribune about the Foothills trail and an update from June 2007.
here's a link to the Foothills Trail Coalition website.
here's a link to the Coalition's newsletters. (The section reporting on the status of neighboring rail-trail projects is really informative.)