How to get from Chamonix to St Martin de belleville?

We are a family of 5 travelling between resorts at the end of January. Any suggestions? It is our first time skiing out of New Zealand so would really appreciate some advice :D

Welcome to J2ski :D The most direct route between the two points is via the Arly Gorge. So Chamonix>Sallanches, then N212 >Megeve> Flumet>Ugine>Albertville. It's a very pretty route, but not a fast road, take your time and enjoy the scenery.
If there is a lot of snow, occasionally this road can be closed to traffic, so check first. The "long" way round is A40 > A41 to Annecy, then N508 to Ugine>Albertville.

From Albertville, head towards Moutiers, and follow the signs to your destination.

Hey there bandit, thanks for this info. We aren't sure whether to bother hiring a car, when looked at the major car hire firms they were pretty pricey(esp with the woeful NZ dollar) and we would only use it for the one day. The train schedule looks cumbersome as well so am really hoping someone knows of either a good transfer company or can recommend a reasonable car hire firm. Am so excited about skiing in both Chamonix and around St Martin, can't wait!!!!!

Without a car, I reckon the most efficient way for you to shuttle between the two resorts would be to take a Chamonix to Geneva airport transfer, and then switch onto

http://www.alpski-bus.com/ who have online reservation, and leave from the airport.

Chamonix transfer companies here...

http://www.chamonix.net/english/transport/index.htm

This transfer will take a while, but you can grab lunch in the airport, they have a good choice of eateries now.