i would go for a AMD athlon Xp ( palomino core ). or a pentium equivalent.
the whole pc would cost about $200, and you would have a good performance for the tasks mentioned.
because, the grafics dont need to be fast.. but if you take a very slow CPU, loading pic's really can take long. so, i reccomend one of the slowest palomino CPU,s , 256Mb SDRAM, a cheap mobo, a 32Mb grafics Card and about a 250/ 350W PSU.
if you buy something like this, you'll have a great pc for doing that stuff.
but if you want the absolute minimum.. i wouldnt go under a P3 450MHz
256Mb RAM, 16 or 32Mb grafics and a 235W PSU.