Similar to Seesmic before them, the Tweetdeck guys have introduced Introduced TweetDeck Web Beta, a webapp version of tweetdeck that doesn't depend on Adobe AIR for it's install. You can sign up with your tweetdeck account for the Beta, but you have to wait until you're chosen to actually participate.
Personally I found the Seesmic webapp the least compelling of their product offerings for some reason, however these days things are going more and more towards webapps so I have high hopes for tweetdeck.