Video editing desktop avchd

I know that this has been asked a million times, all with slightly different versions. Anyways, here goes one more. I am looking to build/buy a new desktop for video editing. I have a canon hf-s10, which records in AVCHD. I was thinking of getting adobe photoshop/premier 9 elements to do video/photo editing.

I am in need of a new computer and have built in the past when it made sense financially. However, it seems like there are some good deals on prebuilt machines as well, approaching the cost of the components.

I would like to spend no more than $500-$600, which I know makes things difficult. The budget is flexible, but if I went above that I would want it to be substantially better. What should I be looking for in a system, component-wise, to do basic video editing? How much will extra cores help premiere 9? And does a video card help with encoding video in premiere 9 elements?

Can you make recommendations regarding components for a system as well.

Costco has a computer that seems to be a good value on the surface for 599.00

AMD Phenom II 955
8 GB RAM
2 TB HD
integrated video
350W PS.

What do you guys think? Any help would be greatly appreciated! STEVE