Craig,
You want to get the air france bus ( I think its number 4 - there are a few different air france bus services into the city). It stops at all the terminals although you will be best of asking at info where exactly the stops are for whatever terminal you are in. If you are flying BA then once you have your luggage come through Duanes, turn left, walk about 150yds and you will come to restaurants. The bus stop is to the right, through some automatic doors. Look at the road markings to see where exactly your bus will stop. Its been a while since i did it so probably best with just asking at information where the stops are rather than relying on my memory!. I used to do it frequently - always worked well.The cost is about 13 euros, you can pay as you board. Should take about 40 minutes in clear traffic, up to 1hr 15 in the rush hour. Runs every 30 minutes but I can't remember what time past the hour. If you have any time to kill there is a friendly Irish pub just around the corner from the bus stop at Gare Montparnasse!
Good Luck,
Gareth
