Do an archive search on the subject and you should come across about a brazillian posts on the subject.

In a nutshell, and Jimshaw's right, learn to use water, soap, local leaves/grasses, and you'll be on par with most of the world. If your hike is long enough, you'll eventually run out of TP, so why not learn to do without from the get-go. You'll save several ounces from you pack weight.
I do sometimes carry a 8" "washrag" cut from that yellow 'camp-towel' stuff from Walmart's camping section. It dries out quickly and is used just like your wash cloths at home. Lean what "lambs ear" is. Soft moss too.
I personally can't think of anything grosser to put in your pack than a weeks worth of used TP, baggie or not...ick.