You'll need to buy one. At least you will if you want a key that is guaranteed to work properly. There are some people here who will reply with some keys (I'm not one of them), but you will almost certainly find that none of them are any good. Same goes for the sites that offer keys or key generators. And not only are the keys unlikely to work, these sites are also common sources of viruses and other malware. Since Microsoft wants you to be using Windows 7 now, you can't buy keys from them any longer, but you can find copies of XP from many vendors. (Beware of the sites offering very cheap copies of XP on CD, which are frequently counterfeits that don't work. The same is true for sites offering cheap downloads. The keys they supply usually don't work either.)
Have you considered the free alternative operating system Linux? Linux is open-source software, meaning it's completely free to download and use. No costly product keys or activation to avoid. With distributions like Ubuntu
, installation is simple. And once it's running, the graphic interface and operation is very like Windows so it's easy to switch. There are free open-source programs like OpenOffice
(a replacement for MS Office) or GIMP
(a Photoshop-like image program), as well as CD/DVD burning software, sound software, CAD programs and many other applications. And using a program called WINE many Widows applications can run directly. It's worth a look.
Thanks for using Fixya!