--This is just a guide to download TBC/WoW, you still will have to buy* the disks to upgrade your account and play.
In the past few days, I've seen a few people ask how to do this because they've gone and lost their disks, or scratched disk 3 or something, so I decided to post this.
So, here is a step-by-step guide on how to download World of Warcraft, and The Burning Crusade via Worldofwarcraft.com/WoW-europe.com
1) Click 'Account Management' on the quick-link bar on the Right of the screen.
2) Log in using real WoW info.
3) Click on 'Download Burning Crusade'
4) For TBC, click the link of the language/system you want it to be downloaded in.
5) Scroll down for Classic WoW download. Click the Language/system you want.
Enjoy.
I'm guessing its the same for the US site, but since I only have an EU account, I wouldnt know.
*buy is a loose term