My Suggestion:
Call Dell/Gateway/HP (whoever "floats" your boat per se)
Ask for the business "dept". VERY FEW businesses are going to upgrade to Vista in the near future because of the cost of deployment.
The people on the phone I am sure will know exactly what to do and get a good laptop with XP on it.
"Brick & Mortar" stores like CircuitCity, BestBuy and such, they cater to the "Moms & Pops" who have no idea (usually) of the difference between Vista and XP and just want something to get on the internet. Thus, they will carry what is easiest to put on the shelf, which right now is the newest OS, Vista.
On the flipside, most businesses will RARELY shop for their computers in BestBuy. They call a major OEM like Dell, and get a computer with the exact Operating System they need. Dell & Gateway know this, and they will put XP on a desktop/laptop for your boss.