windows xp on parallels

I have bought a mac shortly. I installed a free trial of parrallels and then installed windows xp. It all ran nice and smoothly. But now I bought parallels and reinstalled it on my mac, expecting that it would just update and make the validation of the program. What happened is that when I tried to open windows it asked for the serial number. My doubt is, do I just have to write down the serial number of windows and everything will work just fine? or will I have to reinstall it or format it and all the programs I had running with windows?

I would really appreciate if anyone could help me with this.

thanx

What happened is that Windows "saw" new hardware when you installed your purchased copy of Parallels. It's asking you to activate again. Go ahead and activate over the internet. If it refuses to activate that way, you'll need to call the MS automated activation center and do it from there.

Regards.

thank you very much for your help.

Regards