Quote - ..Should I work with spot light and atmosphere only?

I guess using a spot and atmosphere may give more accurate results.  Somewhere around here, there is a really good tutorial on doing lightbeams coming through windows and such.  IIRC, the promo-pic for that is something like a church, abbey or long/wide hall with mulitple widows on the right-hand side and light streaming through them.

For a quick and dirty way, you may be able to get a hi-res planar primitive and assign a transmap to it that is in the shape of your lightbeam.  Position that where you want it and then muck around with some materials settings in order to get it looking right.  Something as easy as a light texture with transparency bumped almost all the way up with a transmap (to give it a triangular/whatever shape) may suit your needs.

I think something like that would give a workable, and very easily directed solution.  I'm not big into the whole materials thing though so you'll have to fiddle with that.  What I know is due to trial and error with a lot of errors and trials... :)