There is only one guy who installed a supercharger in his sienna. If I remember correctly, he has it installed in his '98 model. He has a lot of pictures of the installation and very detailed instructions of how to do it.
Most of the information is posted in the other Sienna website www.siennaclub.org. After going here, search the forums for 98-03 Siennas and his id is nad431. He is also a member of this website toyota nation but I don't think he has as much info here as he does at the other website.
Then here is a dyno run he did with some guys out in Califironia somewhere. He hit 195 and some change at the wheels when he dynoed it. Not sure what factory is at the wheels but should be close to waht the Camry and all others with 1MZ have.