If you go the Canopus route what that gives you is a faster way to edit. Or let me put it this way, you can capture your video using the Canopus codec and can edit more layers faster in realtime. One thing it wont do is allow you to capture video any faster then a regular firewire card will.
Firewire or USB-2 they capture at the same data rates, even tho firewire was created specifically for DV and moves DV more efficiently. There is also the 1394b route, or firewire-8, that can sustain data rates of twice that of regular 1394a firewire, or USB-2. The coming USB-3 is going to have a totally obscene data rate of around 3 gigs a second.
Sound confusing? If you have a fairly new computer and dont want to edit a lot then get a cheap firewire card. Most new computers have them built into the motherboard. The Canopus route is a great way to go if you want to start editing. I use Canopus products and being able to edit in so much real time is a big help for the long form videos I do. Canopus is also known for their excellent drivers and customer service. However I dont know what the scene is with Vista and Canopus.