Although it does not belong here
i can tell you some notes:
For Blender 2.5 you need luxblend25(lb25) + exporterframwork(ef).
Install it best in an external created scriptsfolder/io to which you point in preferences of blender ( scriptspath )
make sure you have matched versions, cause Blender is undergoing api-changes every day atm.
New: you need LuxRender build from sept_09_2010 due some actual changes
- lb25: http://src.luxrender.net/luxblend25/archive/tip.zip
-ef: http://github.com/doughammond/exporterf ... all/master
and a blender2.5 > revision 31838
Please report in this thread buildrelated stuff next time, your problems have nothing to do with this. Edit: Bump for build of sept_09