I used this method with a closed beta key. I have no idea whether or not you can yet access the patch servers with an open beta one, but it's probably worth a shot
1. Download the torrent file and open with whatever torrent manager gets you off. I, like the toolbox I am, prefer uTorrent.
2. When prompted to choose which files to download, check only those pertaining to the patcher. They're pretty obvious.
3. When the torrent finishes [it's only a meg and should take no more the a minute or two] navigate to the folder you downloaded it to, and run the patcher.
4. ????????????
5. Profit.