so you already have a 7" screen in your dashboard? is it a VGA monitor or just composite (RCA)?
it should work fine with an external VGA monitor, it should switch to it by default as long as you connect it before turning the laptop on.
what are the specs on the laptop? upgrading RAM is easy, but the processors are usually soldered to the motherboard, making upgrades impossible (unless you have one of the few models that use a slot).
your specs may be fine the way they are... I use an old Dell Inspiron 8000 (392MB ram, 650MHz PentiumIII) and it runs music/video software, GPS software (iguidance4), and engine diagnostic software with no problem. once you tweak windows you'd be surprised how fast an "old&slow" computer can be
