Have you confirmed your DVD CD/RW combination is compatable with XP? There is still a suprising amount of hardware that will not work correctly with XP!
Assuming this is OK, rightclick My Computer; Properties; Hardware; Device Manager; and open up your DVD, now select settings, and make sure Auto insertification is ticked.
Assuming that is OK, now check the Samsung web site. They have a facility for you to download a small program, and it will check the status of the firmware on your drive. If it needs updating, it will confirm with you, and then download the revised file and update the device for you.