Current specs are:
Intel Q9400 quad core
8GB RAM (this is the max for the motherboard)
750GB SATA drive
There's no consistency to it, and if you ask me, it's more related to what other software you have installed than what your hardware configuration is. But in principle, any decent ATI or nVidia card with, say, 256 MB or more RAM should do fine.
A few useful tips though: Don't install the driver on the disk - that's old. Get the newest from ATIs or nVidias website.
Remove all 3rd party plugins, especially from Nik. Reinstall updated plugins later.
Update DirectX. What else? I'm sure I forgot something...