In 99% there is no way to downgrade laptop with Vista to XP. I tried many times on Sony, HP, Acer(don't even think about buying) and Toshiba and there isn't enough of drivers. If You have one at home and You know there are drivers for xp on the website, think again.
I spoke with agents from all these barnds and all didn't know what to do. Drivers aren't the only thing to install winXP. Let's say, you will go to Best Buy and ask to downgrade any laptop. They will charge You for the OS and service and will say that even if they succeed they won't give You warranty of working.
Beside that if You try to downgrade OS, You won't get any software that you have with Vista.
aka DJ Mad