Macs laptops are acctually fairly competatively priced featurewise with Windows laptops, but lose a bit of ground pricewise with desktops. The benchmarks on the new intel dual processor macs look awesome and if I found a couple thousand dollars on the ground I would totally buy one heh.
The AMD processors have better gaming benchmarks than the pentiums, and the Athlon you've listed is rated higher than the opteron or whatever it is.
So, if you want a mac, go with one of the new intel based ones, they look screamin'. And if you want a PC I'd reccomend the Athlon.
-TV