what is the best way to create terrains for 3dgs projects.
i need a little larger multi textured terrains.
can i use med or is there any other good softwares to export from ?

(terragen,etc)

also i can i export heighmaps & textures from maya also ?

it's the best to paint the heigh-and colormap by hand imho and then import it to a model editor of you choise.

actually you can do it very easily through MED. Just import -> terrain from image (must be 8 bit grayscale).

Then adjust the amount of polys you need (between 200 - 300) BUT not too many or the engine will chug.

Then apply a coloured texture (based off your greyscale) and you're done!

Hope this helps you.