Don't Do It!
There has been at least one poster here that had a sunroof put in by the dealer and it was horrible.
When I first test drove mine, the sales guy told me that Pontiac would never be able to put one in because there is a "beam" right in the middle of the roof - you can see the ridge in the head liner. Even if you get passed that, he claims that the loss in rigidity -and- change in cabin pressure can result in the windshield popping out.
So if sunroof is a "must have" for you, I'd really suggest looking at a different car.