No, you don't have to have a Twitter account to use TweetDeck. You can use TweetDeck with just a Facebook, MySpace OR Twitter account, or any combination of the three.

To start using TweetDeck, just select the button on the Welcome screen corresponding to the type of account you wish to start with (you can always add accounts from other services later).

Then follow the on-screen instructions to log in to your account and set up the initial columns in TweetDeck.