Photo and video editing programs eat RAM - if you're working with really large photos / more than one photo at a time 2GB will be beneficial, 1GB is the absolute minimum for your needs I'd say.
As for the rest of the system, a large HDD for storage, Core 2 Duo CPU and a half-decent graphics card (if you're not playing games cut back a little on the graphics card and go with more / better RAM and / or a better CPU) should be the basis of your system.