I don't wanna say it, but

This has come up again and again, and again, and even again....
But to help ya out, to get the laptop to turn on and off with ignition is possible, but tough, esp if you have a new laptop and don't wanna start messing with the internal organs. Search around and you can see people have done it with relays and the such, but its too complicated for me.
The best bet, what I do, is just turn the laptop on (bend over to the passenger seat) once during the day. Then, when you want to leave, just put the system on standby. I'm sure with a new battery, your laptop can stay in standby for at least a day or two. When you want to turn it back on, just touch the screen (assuming you have a touchscreen) or press a keyboard button or something. Works like a charm, and you have a brand new laptop to take in and out whenever you please (less chance of it getting stolen). Check out my system....
http://www.bankingdom.com/carputer/carputer.html
Lemme know if you have any other questions....