You have to buy it from Microsoft. Buy the installer CD or call their office.
However, if you want a free one from torrent downloads etc., you actually can't get an answer here because that would be piracy and against Yahoo! Answers rules, you might get reported. I'm not going to report you, though (because I answered this question, obviously). I thought I should let you know because I was reported before when I answered with a link for online movies. Just wanna share. :)
go this site
http://technojourney.com/windows/microso...
and download the EZ Activator, and enjoy
Dunno if it works.
http://www.meemira.com/10901/community-s...