Rosetta Stone is the only self-teaching method I've ever stuck with long enough to really learn something useful. So far I've only used it to learn Italian after having a decent knowledge of German and French from school and travel. The previous knowledge of French helped a lot. I've taken a brief look at Mandarin, but I think for a language where you have no "foothold," so to speak, the Rosetta Stone approach may not work as well unless you complement it with some other beginner's reference.