Peter Guthrie has added part 2 to his VRay grass tutorial that I mentioned in a previous post
You can find the updated tutorial here: link
The results are amazing! He uses the VRayScatter plugin, but you can also use this free scatter plugin by Peter Watje: (link) I've used this free scatter plugin before and it works pretty well. The nice thing about it is that you can scatter VRayProxy objects as instances.