To install tweetdeck first we need adobeair in our sustem download the deb file from this link
then from the downloaded directory issue the following command to install the deb fil
sudo dpkg -i adobeair.deb
Then go to tweetdecks site http://www.tweetdeck.com/. Click the “Desktop” link on the website.Then select download its free.After the download/install Adobe Air will ask you whether you will open, save or cancel the downloaded application.If you click open it will install tweetdeck automatically.During the installation TweetDeck will provide options of having a shortcut to your desktop and launching TweetDeck after installation.I just selected launch the application.