Not a bad tip with Crutchfield, but I'm gonna say 'no' to the Best Buy idea. Open up the yellow pages and find car audio & security shops. Visit a few and see what they can do.
Best Buy rarely has the individual talent to do anything besides basic installations very well. I see 'multimedia' and you won't be able to watch anything while the car is moving, so I bet you'll be interested in LCDs in the rear of the car. And it's at that point that the local specialists will be able to help. :)
They should be able to install in 1-2 days. I would expect a few hundred in custom labor, but you may be able to get a much better deal on the equipment to offset that somewhat-- Crutchfield sells at MSRP and sometimes local shops will be considerably cheaper. (Sometimes not, though!)