yeah it should be more than powerful enough to power your system.
As far as the Audigy, go for the cheaper one. I have yet to see a real benefit in the newer models. The audigy 2 ZS platinum is a great card.
also that mobo you picked is a mini-atx board. you need to look at the PK5/PK5 Deluxehttp://www.xbitlabs.com/articles/mai...overclock.html
There is one review. just type P5K review & you will see a ton of reviews, all of them good. It offeres excellent upgradability. It is future proof, being able to support the new 1333 FSB procs & 1333MHz + memory in it's native mode.
you can get the regular p5k which drops wifi & a few other small things. You can run comparisons on the Asus website.