Sorry for the delayed response, I have not been checking my email.
A few weeks ago, I would have believed that any computer would keep it possible to downgrade to XP without any problems, until a CH member posted a topic about it.
He claimed that he was unable to run XP correctly, since some of the hardware in his computer did not have an XP driver.
Most manufacture OEM's will not supply a full list of compatible drivers available for all operating systems. (since they are cheap and stuck up)
If you go to the manufacturer of the hardware itself, a lot of the times, they will not help you with getting the compatible driver, since the OEM has in their contract that all support be directed to them. (Yes, I happen to be talking about the jerks down at Dell)
Now, this does not mean that its impossible to get it to work, but it does not mean that its compatible.