ooooh the ultimate debate - but its an easy choice.
Some would say Macs are over priced and u only paying for a lable. I work with both. The office i use a mac, at home a pc.
For you though - If u ewanna edit on a laptop buy a mac and get Final Cut Pro. - You know it will work, it will be stable and you'll be laughing.
You will need to buy an external drive. As macs now support firewire800 go that route, otnerwise firewire400 or usb2 - dont be tempted by a regualr usb drive. - It wont be fast eneough.
All in all - Even though there are some really nicely specced windows laptops out there tbey just are not good eneough. They are not designed to handle vide editing. MAcs on the other had - Well the G4 laptops were designed with Final Cut Pro in mind.
I am hoping to buy my own mac soon, oooh G5!! At home I'll have both a highend PC and a G5 - YAY!!
Here's a link for a place I bought my office mac from - they were ace and about hafway down this page there is a laptop bundle.
http://www.macdvd.co.uk/bundles.htm
Good luck