You're off topic for this forum, which is dedicated to Windows Live OneCare.
You don't want to get XP Antivirus 2008 back, as it is a scam product - assuming that you are referring to a product that is advertised via a pop-up on your machine that states that the machine is infected and directs you to purchase a product to clean your system.
You can get a 90 day free trial of OneCare at http://onecare.live.com or you can get any number of legitimate security products, including a free copy of Avast for your protection - http://www.avast.com
-steve