If you REALLY want XP...they will install it for you at the store if you ask, and want to pay a bit extra (usually $99).
I do NOT recommend that configuration, Windows 7 is about to ship and MS will put the screws to anyone still using XP (no support, no upgrade discounts, etc.)
Vista/Windows 7 has gotten most of its bugs squashed and runs fine, and gives you access to much more RAM. Anybody still using XP on a NEW system when Windows 7 ships is just being silly. (XP is fine for existing systems that are not intended to be upgraded much more, I've got several myself).
The first system, you should be able to walk in and buy off the shelf. The second is an online purchase. Either one will be fine for what you said you needed.
$899
http://www.bestbuy.com/site/olspage....2180440 29168
$899
http://www.bestbuy.com/site/olspage....2180121 94815