Quad-core Mac Pro, 8GB RAM (order the RAM from a third party supplier like Other World Computing or you’ll spend a bundle), video card is not important. Get (at minimum) a 22″ widescreen LCD monitor – Dell has great monitors for great prices. You would be even better off having a pair of these – one for your work area and palettes, and one just for the comp window so that you can preview HD comps at 100%.
You would also be wise to invest in three extra 500GB drives in RAID 0 configuration, ideally with a proper RAID card rather than using OSX’s built-in software RAID. This 1.5TB array would be perfect for your media – fast access since it’s RAID, plus plenty of room for those large files.
I know Windows users will say otherwise, but after years of trial and error I think macs are the way to go, especially with HD work. Dollar for dollar, a PC of comparable specs and build quality to a mac will cost you the same (if not more) and macs hold their value MUCH longer than any PC could hope to. Also, you would need 64-bit Windows to access the amount of RAM macs can, and Windows 64 has heaps of issues.
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com