No such thing as Vista/XP, it's one or the other. To move your licensed copy of Creative Suite you first uninstall it on one machine, making sure to mark the box that releases your registration for reuse. Then install on the new machine. If you don't have media then you need to purchase it.
Read sections 2.5 and 2.6 of the End User License Agreement and you will have your answer. It does allow for installing a second copy under certain conditions for personal home use. The file mentioned above is in multiple languages so you will have to scroll until you see the text in your language.