It is a good idea to get an early start. If at all possible try to take a short, instructor led class first. There are a lot of training companies that offer 2 week or 4 week classes. By every measure Mandarin is completely different than any Latin based language. Understanding those differences and learning a few key phrases correctly is perhaps the best head start. It is so different from English that having an instructor may be much more valuable than any book or CD in the beginning. The biggest difference is the importance of the tones, Mandarin is a tonal language and it takes some people a long time to be able to hear the tones well.
If I had to do it over, I would wait at least 6 months before taking any serious Mandarin classes just because it can take along time for your ears to get used to the tones. You may find that there is a lot more English spoken here than you would expect (but you'll also find many situations where English is of no help what so ever).
To make your total experience as good as possible in the beginning consider putting more effort into learning about the cultural differences. It's like you have to understand what's going on before you can communicate about what's going on. Just wait, you'll see what I mean
Reading 3 books on cultural differences is probably more helpful than reading 3 books on learning the language in the beginning.
The Rosetta CD's are very thorough but the accompanying documentation is very poor, and the price is completely ridiculous. People say you can download it for free on bit torrent sites if you're into that sort of thing. A $30 book with one or two CD's will be as helpful as the $200 Rosetta series, especially if you do not have a bit of instructor led training. Maybe your company will pay for an ~80 hour class.
