I'm on a somewhat tight budget, but this is what I'm buying from Newegg:
Intel Q6600 Core2Duo (2.4GHz quad-core)
Gigabyte G31 Motherboard
4x2GB G.Skill DDR2-800 (8GB total)
Decent PSU, case, DVD/RW, etc.
All for under $500 shipped.
I already have a license for Vista Ultimate 64-bit and a NVIDIA 7950GT that I'm planning to use. I've got a whole mess of hard drives to use as well. I'm thinking of overclocking the Q6600 to 3.2GHz or so - I've read that's an easy speed to reach without getting crazy with extra cooling required - the motherboard I chose is supposed to be good for that.
Will this setup perform well with A12? Any other suggestions?