Personally I am an amd fan, but if you go 64 bit make sure you are using a socket 939 board. Otherwise you are buying into an old form factor.
for shopping I use pricewatch
I also shop at www.geeks.com
has some decent deals.
most boards come with on board sound which sounds decent. If you want to upgrade the sound card expect to spend a bit. honestly I took my Soundblaster live card out after a couple of years since the onboard was sufficent. for video cards the $50-$60 video cards are pretty decent if you don't game. spend the few extra dollars and go sata on the hd. you may want to buy a firewire card as opposed to having one on-board, since the boards that have them cost more than the price difference. do some shopping and tell us what you are looking at and we can give you advice from there.