If you want that great, irregular uncut grass that some other programs have, forget it.
We can only do the equivalent of indoor/outdoor carpet.
Here's a link to some great flat grass that Neil robinson posted:
http://archicad-talk.graphisoft.com/viewtopic.php?p=51102&highlight=grass#51102
You can use the texture as a displacement map - it isn't that bad..... just don't get too close.
Dwight Atkinson