Installing windows XP original license

My questions is about the following cituation;
I have an IBM think Centre with a valid windows XP pro license (windows Sticker on tower) but I do not have the original cd, how do I go about re installing windows xp using the license on the sticker?
also I would like to understan a little bit more about windows xp diferent releases, I would apreciate if someone can point me to a link were I could get some info on that issue.
Thanks guys!