First of all, the WTF folder goes directly inside your WoW folder, not inside the Data folder.
Code:
World of Warcraft\WTF
Second, since that UI page does not have instructions for installing, I will tell you this also:
- Replace your Interface folder with the one that comes with the UI (don't just put the UI folders inside your current Interface\AddOns folder)
- Make sure to rename the folders inside of the WTF folder to match your account name, your server, and your character
Third, that UI has not been updated since December of last year. You will need to updated the addons included and, at the very least, check "Load Out of Date Addons" at the addon selection screen.
If you don't wish to have to deal with updating the addons, then I suggest maybe trying this UI:
http://www.wowinterface.com/download...blo3theme.html