Quickly entering multiple recipients

I recorded a little screencast to show what I mean, because it's hard for me to put into words: I'd like a way to be able to move between address fields on the new message compose window using the keyboard, and not having to use the mouse. If I'm adding people quickly, I want to type maybe a first name (or the part of an email address), hit tab or comma (or something) and have the cursor be in a field where I can add another address.

http://rp-network.com/blogstuff/postb...

I'm sorry if I'm not being clear, or if there's a way to do this and I'm just unaware. Thanks!