Computer to do editing.

Alright now that my mind is set on getting the FX7 I will be looking to get a mac to use strictly as an editing machine. ALl I would keep on it is the latest Final Cut and whatever film I am working on... Ideally I would like to have a laptop but from what I'm hearing going to a laptop would limit me. So the question is what is the minimum required computer speed and ram amount to be able to edit anything without hassle??? I will be buying used so keep that in mind. If desktop is DEFINITIVELY the way to go I don't mind doing it but if I can get a laptop that would do the same without a hitch than that would be ideal. So basically I need specs, cpu speed, ram, video card, etc