Installing SLG: Graphicall Method
From LuxRender Wiki
Graphicall is a website where you can download test builds of Blender. Make sure that the build matches your operating system (Windows/OS X/Linux) and operating system version (32bit/64bit). And most importantly, check that SLG is included! As of December 2010, a Blender build for Windows that includes SLG has been made available by filiciss.
After downloading the build, unzip it. On Windows, the recommended place would be the "Program Files" folder. On 64bit versions of windows take care with the "Program Files (x86)" folder as this is only for 32bit programs. So when you have a 64Bit Windows and a 64 Bit version of Blender do not put it in the "Program Files (x86)" folder, although with the 32bit version this would be correct.
If you encounter any problems regarding the .NET libraries you might need to download them at microsoft.com. For other problems regarding builds provided at graphicall.org, please ask the Graphicall community.
(Windows specific) Before you start Blender check the Properties. To avoid problems when Blender or SLG tries writing image files to protected location, you could consider running the program as administrator.
Sorry for german picture.
(The next time you restart Blender,) SmallLuxGPU should be available as an option in the "Engine to use for rendering" selection box.
To use the SmallLuxGPU Blender 2.5 plug-in, select SmallLuxGPU in the "Engine to use for rendering" selection box in the info panel (typically located at the top of the Blender window)
When rendering, the currently selected scene is exported.
To make a quick test select the cube of the Blender start scene. Go to the material tab. Add a New material, crank up the Emission, and press F12. Now you should see a light cube. By pressing 1,2,3 or 0 you can change the Render mode.