Paint shop pro http://www.corel.com/servlet/Satell.../Display&pfid=1047024307383&pid=1047023911984 and Photoshop http://www.adobe.com/digitalimag/main.html Both support layers and transparency and will enable you to add backgrounds to images as well as anything else you can imagine doing to an image.
Photoshop is the best program I've evel laid my hands on and it keeps getting better. CS 2 (newest version) is no exception.
