Yes, assuming you have a double din like my 99, you can put most aftermarket units in.....however, they are incredibly expensive for what you get....and they don't have detachable faces, etc., making them more likely to be stolen.
The Alpine, in my opinion is the best, because you can have the nav, which plugs in like a cartridge, along with the DVD/CD player.
Other less expensive units use the CD slot for the nav, which means while you are running nav, you can't be running a DVD/CD. That bites in my opinion.
FWIW, I just bought a Garmin Nuvi 200W for $199, and I love it. The alpine would cost you about $1000 or so.