Lost the windows XP cd, hrm. As long as you have your CD key for it you should be ok. I hope ya have your CD key. If not, their are some ways that are legal to get back missing or lost copy's from microsoft.
You are also very smart for your age, and remind yourself of what i would have been doing to computers a few years ago. If you still have your CD key, and cannot get get another CD key, i can help ya.