best way to improve HD video editing is to put the content on a fast external drive (firewire 800 or eSata) with a decent 7200rpm drive.
this tends to be the major limiting factor. careful with processor speeds as most video editing packages (even the pro ones) are useless at multithreading (using more than one processor at a time) whereas mac tends to be a lot better. adding another core to the processor will make no difference if it’s not used, better to have less faster cores than more slower ones if you get my drift. For instance, put my vaio next to a macbook pro and mine will sit with 2 processors running at 80-90% whilst rendering and the MBP will run all 4 at 100%.
like i said, HD read/write speeds really does tend to be the major problem with editing on laptop, most other problems stem form this.
I use a Sony VPCEC1S1E (huge) but only really because it has a huge full HD screen and loads of video memory.