I had an Acura TL (had to sell it for a mini-van, man - that hurt) with a built in NAV and loved it. When I started driving my truck, I picked up a Garmin Nuvi. Having experienced both, go the portable route. They are cheaper, better, easier to upgrade, and transferable between cars (friends, rentals, you name it...).
My vote - save the 1,200 (that's a nice laptop!)
-B