That is correct.
There are actually units that will not accept XP, because of firmware version, that is installed at the factory.
But I do not doubt that there is a way to bypass that feature.
I would try bulk erasing the hard drive, or putting a totally new HDD in. Not Verified, however.
Also you might be able to get an older version of the firmware that allows XP.
But, what many XP fans do not realize is, Win 7 has much clearer video, and it's not "that" bad. There are actually some things to like about it. It ran all my older applications except Roxio. It interfaced to all my 5 year old hardware too.
(check manufacturer website for win 7 drivers, to run your old hardware)
But, the real reason I like 7 is the much clearer video, it was worth it to me for that reason.