Septimus said:
Pentium 4D 3.2GHz x2 -> Core 2 Quad Q8200
1GB DDR1 -> 6GB DDR2
250GBx2 HD -> 640GB x1 HD
x550 -> uh...nothin
Not bad, really. I mean, if you are not using those HDs in raid, then the new hard drive is a clear upgrade. The RAM is a huge upgrade (although Photoshop can't really use more than 2GB unless you run CS4 64bit). You can probably just carry over the videocard, if it's PCIe, since all the new one has is onboard video.
It's not top of the line or anything, but the CPU is pretty fast and there's a lot of memory, so it sort of fits your bill regardless. Vista 64 is pretty good these days so I don't think you would have any issues there, although you might want to check status on any pro level apps you use.
I don't think you could build the same box for cheaper;
Vista 64 OEM ~140
Q8200 ~250 (Phenom 2 X3 is around ~200)
RAM ~80
Cheap HD ~50
MB/PSU/Case/Card reader can't quite magically fit in the remaining ~130 unless you go really bargain basement, so I'd say it's a reasonable purchase for your needs. The only problem I have is that I can't tell if it has a PCI express slot or not. If it doesn't, well, you'll never be putting a video card in there...
Anyway, there could be some comparable and more flexible options on NCIX if you tinker around...