There is plenty of software to build virtual Lego models with your Mac or PC. These applications use properly defined Lego parts data in the form of 3d objects to help you create a lego scene or instruction booklet of a Lego model. Just for fun, I decided to render some of those bricks and turn them into Photoshop brushes.
These are the programs I used : LDraw (not exactly a program but it is long to explain), MLCad (to distribute a group of bricks all over a virtual floor), L3P and L3PAO (to translate MLCad file into a POVRay file) and POVRay (to render the scene). These applications are free, but they are somewhat difficult to use if you are technically challenged. After rendering the scene, I opened it with Adobe Photoshop and started to create each brush. Follow the link below to read the complete tutorial that will teach you how to create a Lego Bricks Photoshop brushes set.
By the way, and this has little to do with this tutorial, take a look at the effect I applied to a photo I took some time ago in my visit to the Disney Downtown Lego Store.