Oh ok, well you'll be happy to know that I used an ADVC-1394 without any problems on my nforce1 board. Well, other than the bug with SP1 on XP, but that's a Canopus/Microsoft problem.
You'll also be glad to ditch Studio 8, I hated it. I returned the Pinnacle Studio Deluxe because Studio 8 was so buggy and the card *only* worked with Studio.
Compatibility problems with AMD based systems used for video editing really only come into play when using VIA based motherboards, but that extends beyond just video editing. However, there is a document on Matrox's website stating that some of their boards are incompatible with Nforce boards. I used a RT2500 for a while, but never got to try it on the nforce so I can't attest to that.
Canopus themselves sell Athlon based systems that come with the DVstorm2, so I doubt you'll have any problem there. Steer clear of VIA, which should be a no brainer especially considering how affordable the nforce boards are, and you'll be fine.
If you're still debating on which processor to get, find some reviews that extensively test the encoding speeds of the P4 versus the Athlons. I'll suggest Toms as a place to start, but I know there'll be a lot of response posts about how he's biased toward Intel, so take them for what they're worth. I do see a good bit of performance increase with the realtime effects previews in Premier 6.5 with the P4 that I upgraded to, but that's somewhat to be expected considering the increase in clock speed.
Sorry for the long post...