eduarbermon,
You can aquire a genuine Windows XP product license by purchasing online at Microsoft or at a local customer
retailer.
http://www.microsoft.com/windowsxp/pro/howtobuy/default.mspx
If you are uncertain as to the authenticity of a Windows XP copy or having issues with reinstallation, please follow the instructions provided by Stephen Holm and repost back into this thread.
Thank you,
Lori MS