If you don't already got Songbird, download it and follow the setup guide.
Open a new tab
Now, with Songbird installed, open a new tab. You can either press Ctrl + t, or in the menu choose: File->New tab.
Did you do as i said? Good! Lets move on:
Now in the address field enter: http://addons.songbirdnest.com/addon/1485 and click the Install button.
Press "Install Now"
A popup box will ask if you are sure you want to install this extension, just click "Install Now".
Now with the extension installed, Songbird asks us to restart, so we click "Restart Songbird".
Now you're ready to use Now Chirping. You're left bottom of Songbird should now look a lot like this:
Now that you've succesfully installed Now Chirping, I suggest that you take a look at the tutorial, so you can learn to use Now Chirping