If you are having a very slow download of the patch, I am providing you a link to my web site where you can download it quickly:
http://www.ascotwoods.com/WoW-2.0.12...-Win-patch.zip
Unzip the file into your "c:\program files\World of Warcraft\Patch" directory. It should create a sub directory. Then just run WoW and it should detect the patch and install it.