kissmysquirrel,
One technique I use for a downwind departure, if you have a wee bit of room. Hover into wind, as you lower the nose to accelerate and begin to move (into wind), progressively begin to turn downwind and continue to lower the nose and accelerate throughout the turn downwind. You will be through translational lift prior to being downwind and away you go. Of course your groundspeed is fast as you accelerate and turn downwind. In a light helicopter you maybe only need 20m in front of you and about 50-75m out to the side you are turning.
A direct downwind departure, just be prepared for it to sink out as you accelerate, catch up with the wind and come out of translational lift. Be ready on the power and dont let it sink. You will have a pretty quick groundspeed (maybe 10-15KT + the tailwind) before you regain translational lift as you 'come out the other side'.
Don't forget the climb gradient is not as good and you need more distance for obstacle clearance, as Nick Lappos previously pointed out.