It's nice to see so much activity on this forum however I dont think (although I hope I'm going to be wrong) that you will get much response on this forum about your question.
I've been lurking around the excellent Sound on Sound PC forum for quite a while now.
http://www.soundonsound.com/forum/postl ... oard=PCMus
There's a sticky at the top that forum where people have been listing dual core setups. In contrast it's worth taking a look at the thread that talks about using Celeron laptops just to see what people can get by on.
I'm going to resist the dual core route for the moment, mainly because all new motherboards are using PCIe. There seems to be issues with some pcie chipsets and some audio software. I'm going to wait until everyone else has been my guinea pig that's before I take the plunge