Heres my '04 Ford Ranger Edge. I went a much diffrent route then most people.
As for fitting something the size of a laptop under the seat..you're probably going to have some trouble with that as previously mentioned. I have an ATX power supply under the seat, and width wise, it's a pretty close fit.
And the stock Edge H/U (at least for an '04) does not have aux-in. Personally, I bought a H/U with aux-in..I wanted one for fm radio and thoes 5 minute drives where you really don't need the computer.