you need to search for "cingular internet". it's one of the ways to get wireless inetrnet
tv antennas in the car don't get the best reception while moving. few people have got this to work.
since you have the computers, the main cost will be the screens. and you can buy screens already installed in headrests
you can power 12 laptops if you want. read the FAQ's on power supplies
better yet, read these threads