Here is a demonstration map with a poorly textured house, and a completely working lightning system.
Also, if you're in the water when the lightning strikes, you get splattered.
If you'd like to know how to set the lightning up, it's pretty simple. Beams, light entities, and multi_managers.
Anyway, here is the RMF. Have fun
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RMF: http://www.mediafire.com/?hwjyf771oi0otz9
BSP: http://www.mediafire.com/?zclanf58rc8551k