http://jhaywood.com/maxScripts.htm I have a script that does just that in my pack-'o-scripts: Look At Viewport "Forces an object to always face the viewport. A modifier is added to the object that includes options to turn off the auto look at behavior, or to enable it only for certain types of viewports."
AFAIK you need a camera. Assign a Lookat controller to the object's rotation, choose the camera as the target. Do a search for "billboard" on http://www.scriptspot.com, there are a few scripts that automate this.