I'm creating a scene with buildings at night and have placed lights inside the building so that it will show out through windows, doorways etc. Ive tried spot and point but when I render nothing shines through the openings.
I need some guidance!

Some clarification please.
How is the building created? What do you expect to see?

If the building is created with actual openings the light will shine out. If the building is created with blocks and texture maps no light will shine out. If the building is created with transparency maps light might shine out if the correct options are set. Of course light will only show if it actually his anything unless you are using volumetric lights.

Most buildings are created as blocks with texture maps, this is light on polygons and will create the correct effect. In general light inside buildings rarely lights up anything outside of the building so to create the illusion of lighted windows and door the texture map has to be changed or an additional map with the lighted areas has to added.

or fake it by putting omni lights outside the window to mimic the light spilling out but it'll be a pain in the butt to get them all looking right

Realised that my post said the same as jfbeute's, in a different way...!

It's created from a cube primative, then to a vertex model, openings are actual openings in the mesh. I think what I need to do is create an interior surface for the light to interact with, and then its the illuminated surface showing not the light itsself. All normals are currently facing out so I guess the light has nothing to illuminate on the inside of the building.

Post wireframes of your building in the scene (use the preview wireframe renderer and take a screenshot.
Is there glass in the windows?
What version of Poser are you using?

Point lights will usually do this job.  Set the Dist Start to about 0.5 and adjust
the Dist End until it looks good from outside.

The wireframe picture as suggested by Muralist will show if other problems
exist.   One big possibility is that the windows were formed by a type of
Boolean cut that doesn't subdivide the mesh.  If the windows are just holes
in one big facet, Poser won't understand them as holes, and won't let light
go through.

Those are certainly "good holes".  :)

The mesh looks clean, built the way Poser likes it.

Point lights should work, with the right settings
of Dist Start and Dist End.

Also, I think you'll need to render with ray-tracing, and set
the lights for ray-traced shadows, to get the best effect.
Depth-mapped shadows don't handle windows and
doors well.

You can make your window glasses separate objects and set them to not cast shadows.