the video card doesn't have that much to do with editing video, so ignore that.
i have, and use, final cut pro on my CD macbook - with 2 gigs of ram - and it works fine for simple edits. the fans only ramp up when i am using compressor to create qt files.
i am actually quite happy with the performance. (editing DV footage)
here is a video i just finished on my macbook:
http://www.bobscottnyc.com/seagirt.mov
that said, if i have a big edit i would do it from my desktop, but for smaller projects, the macbook handles DV editing just fine.
you absolutely need an external drive. this is rule one when it comes to editing video. you keep your editing app on your primary drive, and capture your footage to a secondary drive (weather it be another internal or a external) I capture all of my footage to my OWC Mercury Elite Aluminum Pro (250 gig)
http://eshop.macsales.com/shop/firewire/
hope this helps