Hi Perry,
Go with the Intel Core i7 and an Nvidia display card to take advantage of the GPU-acceleration of Adobe Mercury Playback Engine, and you will edit AVCHD with ease, plus get very fast exports to various formats including H.264 and DVD.
Adobe-approved GPUs are listed here -
http://www.adobe.com/products/premiere/tech-specs.html
If the budget is tight, you can use other cards not on the list and make them work, see this link:http://www.studio1productions.com/Articles/PremiereCS5.htm
Jeff Pulera