A few requirements IMO:
1. Lots of RAM
2. Lots of hard drive storage, with emphasis on average transfer rates rather than seek times
3. A video card with excellent quality AND DVI-out.
4. Processing power.
Not necessarily in that order... The Matrox Parhelia (any kind) will definitely satisfy the third requirement. A RAID 0/5/10 array (in order of price) will give you data protection and additional speed, for the latter 2 array types. 3ware makes some nice IDE RAID cards, but the newer motherboards do have onboard RAID. As for the CPU, I'm partial to AMD, although if you're really set on Intel it doesn't make a big difference.