Of the two system choices you have there go with the Intel setup
As PZEROFGH (what a name) has suggested, you could go with a single core CPU for now, and sock the price difference into a monster of a graphics card. An Opteron 144 should cost about 2/3 of what that X2 3800+ does, and it will overclock like nothing of this world... You can upgrade to dual core on down the road.
You definately want to go with 2gig of RAM, if at all possible. Today's games love their RAM. And the DDR of today holds its own against DDR2... unless you go to the newest and bestest.
As for what graphics card, that's up to you. nVidia is the make of choice around here, but buy what you want. Just don't scrimp of the graphics now, or you'll be sorry later.