The Athlon is definitely a faster processor than the Pentium computer. However, the computer has two less gigs of ram (which is honestly good for most people. I'm a super heavy multi-tasker, but I don't breech 4 gig usage until I'm doing 500 and 1 things AND photo editing. Even then, I only use 4.5 gigs). No GPU is listed, so obviously its integrated graphics.
Ultimately, I'd go for the Athlon based computer. The processor is definitely faster than the Pentium (courtesy of anandtech CPU bench charts
), and 4 gigs is probably going to be more than enough for your use. If not, it costs like $20 to upgrade to 6 gigs?. Throw in a $60 GPU, and you'll have a very nice platform (for when, or if, you decide to go that route).