Keep in mind that I don’t recommend anyone to use a pirated copy of Windows. It is not ethical, and it is also against the law. That being said, I recently came across an interesting Forum post detailing how one can make Microsoft recognize your pirated copy of Windows XP as genuine.
If nothing else I find it curious how easy, apparently, it is to trick Microsoft’s anti-piracy lock. Either they just did a poor job at it, or the guys who found this workaround are pretty clever. The trick consists basically in creating a reg file with some code. Many people claimed that it works like a charm. Go figure.