I'd say quadcore for sure, freaking cheep!.Throw in min 2gb ram (3-4 better),2 Raptors in Raid 0 for os and programs,500gb+ storage with an NAS 1 TB back-up server (I used 4-500 gb generic drives on a rocket raid controller in RAID 5 in old tower for total of 1.5 Terabyte NAS-keeps all my backups-and I'm thinking of throwing a 1TB wireless NAS in my garage to back up the 1st NAS). Paranoid about backups for sure.
I suggest a configuration that includes at least these items:
Quadcore or core 2 duo processor,
Motherboar with FSB 1066MHz support (Asus P5 series),
Memory DDR2 (or DDR3) with 2 or 4 gb (in dual channel),
2 Sata Hard Drives in raid 0,
Graphics card with DDR3.
Assuming that you haven't dealt yet, why don't you just bite the bullet, do the sensible, graphics stuff to the fore thing...and buy an Apple Mac?
Look at the powerbook pro (laptop) or maybe the iMac, but the biggest beast is the MacPro (desktop) but this is kinda budget-dependant.
You won't regret it, I promise you.