Now, why on Earth would you want to do that?
On the product support page ( http://support.acer.com/product/default.aspx?modelId=3680
) the selectable operating systems for driver downloads are all Windows 7.
Did you have Windows XP on this machine before?
Anyways, what happens when you insert your Windows XP install CD, and you reach the point when you can select the disk/partition to install to?