There are so many versions of Windows out there - not only XP, Vista, and 7; not only Home and Pro, Ultimate or Basic or whatever; but also the Corporate, OEM, and Retail; and for each of those, a different media, different manufacturers, and even different vintages. So, suppose you, like I, found a junked computer and revived it, but reinstalled from your own copy of XP Home. During registration, the CD Key on the sticker on the case will not work. The media you have, and the media the computer came with are not the same.

Despite this, you have a legit XP Home license. (I have four of them, collected from junked computers.) You have the computer, and the motherboard. You could call Microsoft... but they may not activate you. If it hasn't happened yet, they will eventually refuse to activate Windows XP.

Enter the hack. While some people like to call MS, some would rather just find a quick, reliable technical solution. That solution is called AntiWPA; to find it, search for it.

AntiWPA works better than the other hacks because it installs a service that fools Windows into thinking it's starting up in Safe Mode. When you boot into Safe Mode, Windows does not check for activation status; that's because the Safe Mode is supposed to allow you to repair anything, including the activation software if it's damaged.

There's also the issue of Windows Genuine Advantage (WGA), which comprises Windows Genuine Validation (WGV), and Windows Genuine Notification (WGN). The way to disable WGA is by allowing WGA to verify that you are a genuine, non-pirated copy of Windows.

The typical solution is to download wga-fix.exe. This little program fools your networking into pointing the WGA's server name to nothing.

Then, you run MGADiag.exe, which is the regular WGA validation tool. The tool will check your system, and then contact the server. The server will fail, but the software's designed to let you succeed when the internet fails. (Presumably, there are millions without internet who run into the WGA issue and need to be validated. It's cheaper to let that shrinking population get validated than to staff up the phone centers to handle the tech support calls. On the other side, as more people get internet MS will catch more pirates via WGA.)

Both these hacks are good because they work in alignment with the economic decisions MS will make, assuring that there's a cost impediment to designing their software to operate differently.

Now that you've read all the crap above, please consider switching to Linux. I'm using Ubuntu and think it's great. It's my main OS at home. There are a few free programs I use so much that I donate money to their projects every year or so. It's great! I'm even starting to evaluate it as a side-grade for Windows 7. It's already a great companion OS for a second computer because it's strong where Windows is weak.