I agree with ACtheTroll, the sticking point will be drivers.
I read an article in a computer magazine the other day about someone who tried to remove Vista and install XP on a new laptop.
After doing the XP install he found that because it was a new laptop many of the hardware components in it did not have XP drivers available.
If you do not have the XP drivers you may find that some of the components in your laptop may not work (or work badly) such as graphics, sound and so on.