Anything should be reasonable, as long as you're not performing complicated filters etc on your pictures. If you go intel, you'd be looking at the 1.46Ghz (T2310?) 'Pentium Dual Core'...basically a lower end laptop core2duo, as minimum, although the more grunt you get, the better for performing more intensive filters and effects on pictures. If you got AMD, you'd be looking 1.9Ghz+. Intel may be preferable though if your work is going to involve any converting etc for the pictures or video work.
2GB of RAM should be easily enough as long as your pictures arent absolutely huge, and you don't open loads of programmes at once whilst photoshopping.