I know the current cars have given up 200 rwhp from last year, but how much lighter are they?
Not sure, but I think the minimum weight hasn't changed. With the lighter engines they probably just pack more ballast.
The Minimum weigh of the car must be 600kg for 2006 and the engines must weigh in at 95kg min as well. For all the other rules just get them from the official FIA site http://www.fia.com/resources/documents/1603301296__2006_F1_TECHNICAL_REGULATIONS.pdf 59pages, go nuts