Use some lightfog on a spotlight to create the effect of light streaming in through the window. As far as color, use a slight grey.....just go a tiny tad into the "blue country" in your color chooser

Make sure you have shadows turned on for the light and you may have to scale the cone of the light in order to get the "moonlight" to pour into the room. I use the cloud texture for the lightfogs' color by the way

Darkon