If you're going for a Vista system then you'll need a fair amount of RAM, 2Gb min. For games such as COD4 a fairly recent graphics card. I'm managing to run Bros in Arms and Far Cry 2 on a PCI-E Nvidia 7800GT. with no problems. A 500GB HDD should be adequate for your digital photography, depends how much you do. Goes without saying a 450W PSU and a good, well ventilated case. It's your choice but I personally would be more inclined to use XP rather than Vista. Have you considered building your own system? It's not that difficult and you know what's in it.