It's actually called MLCAD. You can get it here: http://www.ldraw.org/
I got it recently, but the parts library seems to be missing a bunch of parts. Maybe I did something wrong Anyhoo, for those that don't know, MLCAD lets you build LEGO models in 3D, you just gotta drag and drop the pieces into the window. Then generate a parts list, and you can just go to bricklink.com, which is pretty much LEGO eBay, to buy the parts to build it in real life