Hi Darren, you should follow Oscar´s and Bryan advices, they now best. I am in Sinaloa (semi-arid), Mexico, but don´t dare to grow that fussy tree. I haven´t tasted them but have only heard good things about their taste. Hope you have both the right soil and weather. I have seen Luc´s rambutan (already in the ground) in Puerto Vallarta and it didn´t look any good, I guess it was his bad soil.

Good luck with your rambutan!.

Leonel. (aka. theofrasto, etc)

Humidity humidity humidity humidity! 80% and greater. Same concept as with growing mangosteens. Enclose the plants in plastic. Bryon from Montoso Gardens suggested this to me a while back and this is even mentioned in Bill Whitman's book. Might even shade them even more. Another thing you might check is the PH of your soil combo. Again, rambutans, like mangosteens, require a more acidic soil...5.5-6.5. Also make sure your temps stay around 85 degrees. One other thing that could play against you is how long have the seeds been out of the fruit? The longer time between fruit and planting, the less chance of germination. The piece below is from Julia Morton:
Propagation
Rambutan seeds, after removal from the fruit and thorough washing, should be planted horizontally with the flattened side downward in order that the seedling will grow straight and have a normal, strong root system.

Hope this helps some. Good luck and let us know how things go.