Getting Started with Bincoin over Tor
Get a copy of Tor
The fastest way to use Tor on Windows is to get one of the Bundles. All are available at  The Browser Bundle contains a copy of Firefox configured to use Tor. The Browser Instant Messaging Bundle contains Firefox and Pidgin, both configured to use Tor. The .exe's are self-extracting archives. You can install wherever you want.
Configuring Bitcoin is straightforward. Open the Settings menu and click Options. Check the box labeled Connect though socks4 proxy. The default proxy IP and port are the correct settings for using Tor.
In the Tor Browser folder that you installed Tor in earlier, there should be a file called Start Tor Browser.exe Run it. The Vidalia Control Panel will open, displaying the status of the Tor connection. It will connect to Tor. When it's done, it will launch the other programs in the bundle, Firefox and Pidgin (if you chose the IM Bundle). Important: If you exit the copy of Firefox that it launches, Vidalia will automatically shut down.
To ensure that Bitcoin is connecting through Tor, exit Bitcoin and reopen it.
Live happily and anonymously ever after
Whenever you need the Bitcoin client, just make sure to start Tor first.