Instructions
Open Windows Explorer and browse to your WoW installation folder. Assuming you didn't change it during installation, it should be c:\Program Files\World of Warcraft\.
Double-click the folder labeled "Data." Locate all files in the directory with "patch" in their names and ".mpq" in their extensions and delete them by right-clicking each one and selecting the "Delete" option.
Return to WoW's main installation folder and double-click Repair.exe. WoW's repair application will launch, notify you that WoW has become corrupted and ask you permission to revert WoW to an earlier version. Approve the request.
Download the v3.32 to v3.3.3 and v3.3a to v3.3.2 patches from Joystiq (Joystiq.com) and run them in the order specified. The former will upgrade WoW from 3.3 to 3.3.2, while the latter will take it up to 3.3.3.