There's a good example of an American woman using IDS with her baby here at http://www.youtube.com/watch?v=XYItFpRFqec

If you live in China, I think that if your baby goes to a regular kindergarten and plays with native Mandarin speakers then "teaching" at a such a young age as 5 months isn't going to be particularly productive. My friend's son is three months old and speaks almost exclusively in Chinese (Chinese mother and ayi, father from New Zealand) with little in the way of formal lessons. If you don't live in China, then a private children's tutor and kindergarten would be the way to go.

Interestingly, a friend of mine was born in Suzhou and was adopted by American parents when he was 4 years old. He only resumed his Chinese studies when he was 16 and now at the age of 24, manages to speak flawless Mandarin.

Language learning really depends on the student and the amount of work that they are willing to put into their studies and getting enough speaking practice - an "early start" will make the work seem less like hard work, but isn't necessary to mastering a language in the long run.