Hi there i am new to this forum. I have done something which i think is similar to what you want to do.i am sending you the web link of my web site which shows what i have done. Have in mind that i used radiosity with a skylight and a direct light, not mental ray. here is the link check it and i can send you the max file if you want.
http://www.3dgs.com/Portfolio/Portfo...ortfolio8.html
Michael