Firewire will absolutely give better results than USB........Then again, I use PCI like some caveman.
Just popped in to say hi and welcome to a fellow Linux/Ardour recordist!
Stay away from 'ANY' VIA chipset motherboard. VIAs are really bad with their faulty interrupt handling. I'm using a AMD X2 4200 with a Gigabyte MB, Nvidia chipset, and it's plenty of speed for me, even with a ton of plugins! However, I am running Linux DAWs and not Windows DAWs (Ardour, Qtractor). I switched from Windows and Samplitude last summer, and have not look back since.
Also, good advice to stay away from the "gamers" video cards. The Windows drivers tend to give them higher priority than the audio. However, there are tools to correct for this somewhat.
No offense to the posts above, but you can get alot more performance out of the intel quads rather than the amd. If I were you I would do the following:
ASUS P5W mobo (it uses the TI chipset for firewire)
Intel 2.66 Quad cor chip
4 gigs of Corsair ram (2x2gig sticks, and very cheap at the moment)
Lian Li Quiet Case with 120mm fans (very quiet)
@ least 2 500 drives for samples and recording, and 1 10,000 rpm drive for your OS (buiy seagate because of reliability, warranty, and price).
Dual head graphics card of your choice (no need to be too fancy for audio. sSomething like an XFX 7300GS is good)
2 IDE drives that can burn DVD's and CD's. If you have the scratch, buy a blue ray drive as well. It will become a great tool for backing up your data.
*IMPORTANT* get a 750W power supply (go bigger if you can afford it).
Definitely get a OEM copy of XP
It sounds like a lot, but you can do all of this for around $1K