if you click on the green box marked drivers and software then enter "Compaq Presario CQ56" it will list all of them
then you need to see if you can match a model up to you system and see if the xp drivers are avalible
if they are you will not have a problem installing xp
if it only lists windows 7 drivers would sugest keeping windows 7
W7 starter is a bit grim you might want to consider an upgrade to W7 home premium 64bit.
do you have a specific need for xp or are you just not getting on with W7.