Guess I missed the first response.
Anyway, check out www.promountainsports.com, Jim has a lot of stuff on there about how most people base their lightweight system. There are many variations on what he shows, but it's a great place to start. I try to shoot for ~35 lbs with overnight gear and rack etc. Of course, once you add beer and other assorted alocholic beverages, that weight limit goes in the pooper.