Usually people just go to torrent sites and download them. As long as you have a valid CD Key (the number on the Certificate of Authenticity sticker, usually on the side of your PC or with a Windows manual), you can legally use a torrented CD, as long as you don't use hacks to break the authentication. I got a torrented CD from my friend, but entered my official COA and activated on the Internet, it worked fine. I had to use it because my computer came with Recovery CD's which insist on factory imaging the whole disk, and I dual-boot with Ubuntu, so those didn't work for me.
Re: Lost XP Disk 
Linear Mode
