WOW you have a LOT TO LEARN.
Create a point light. enable shadows-set it to raytrace shadows, 32 rays, and a low light radius (not zero).
Make it a Mental Ray area light, with samples of 12-15.
Place it outside the window.
Make it emit photons, especially Global Illumination ones.
Now create a spot light- covert to MR Areal Light- with a lot of samples, raytrace shadows- high light radius and 32 shadow rays.
Make the spot light shadows like... dark gray and set the cone angle to like... 150. Place it where the sun would be to make it look like sunlight.
Now take the other light, the point light, move it outside of the window, like, JUST outside of the window, set shadow color to light gray.
Now go to Render Globals- and set the renderer to Mental Ray. Now, turn Final Gather on- 650 samples should be enough
Turn Global Illumination on, 150 accuracy is enough.
Hit render and wait a few hours.
Live the life you love, love the life you live