It took me a while to figure out how to open up two Remote Desktop Connection 2 beta windows without copying the binaries, as one had to do with the previous version. I finally found the answer in the Read Me menu item:
Multiple Sessions:[robg adds: I haven't tested this one, but given it's in the Read Me, I assume it works!]
Remote Desktop Connection Client supports multiple simultaneous Remote Desktop Connection sessions. You can save the connection settings for different Windows-based computers to Remote Desktop Connection settings files, and double-click those files to open multiple sessions independent of each other.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080205023851474