Although Microsoft has stopped selling XP, they will officially support Windows XP until 2014, and EVERY Windows Vista license comes with an implicit downgrade option to XP. And you can still buy Windows XP from Amazon, by the way, and any other vendor on this planet - as long as they have it on stock.
MacBook Pro: Besides the fact that it is still the fastest notebook for Windows Vista, Windows XP also runs extraordinary well on it -> a friend of mine happily uses it every day on his MacBook Pro (in what is called BootCamp), and yes, he plays games on it.
BUT: Only 32-Bit versions of XP are supported by Apple. Which shouldn't be an issue, since you can only squeeze 4 GB RAM in the MacBook Pro anyway, so you won't be needing a 64-Bit OS to take advantage of the hardware. You might have some luck getting 64-Bit Vista running on it, though.
MacBook Pro: Besides the fact that it is still the fastest notebook for Windows Vista, Windows XP also runs extraordinary well on it -> a friend of mine happily uses it every day on his MacBook Pro (in what is called BootCamp), and yes, he plays games on it.
BUT: Only 32-Bit versions of XP are supported by Apple. Which shouldn't be an issue, since you can only squeeze 4 GB RAM in the MacBook Pro anyway, so you won't be needing a 64-Bit OS to take advantage of the hardware. You might have some luck getting 64-Bit Vista running on it, though.