Sun lamp and focus of light. Sun rays???

Can anybody please tell me what tricks can be used to create sun rays onto an object.

I have an object on a table and the ceiling above it has a rooflight.

I want the sun to shine on the object on the table illuminating it, but dont want the sun lighting all of the scene.

Im really after a sun rays effect.

Any suggestions?

I think you want a Halo light see the wiki: http://wiki.blender.org/index.php/Manual/Volumetric_Halos