There is an easier way to find a product key for Windows XP. You don't have to visit to suspicious wares' site which often contains dangerous script. Just Googgling up and you will find one.
It's available because some people has been published their very own product key on the Internet. Whether its publication just an accident or not this dangerous behavior was helped a lot by a free tool from Belarc Advisor which could displays a detailed profile of your installed software, hardware and vulnerabilities in your Web browser.
You can read further on Becareful With Your Private Data