1. Get hold of the latest version of Adobe AIR from this site: http://get.adobe.com/air/
2. Open a terminal, and find the .bin file that you downloaded in step 1.
3. Change the .bin file's permissions so it is executable: chmod +x AdobeAIRInstaller.bin
4. Execute the bin file: ./AdobeAIRInstaller.bin
5. Follow the on screen instructions. (it shouldn't take long)
6. Download the latest version of Twhirl from: http://www.twhirl.org/download
7. If the Adobe AIR installation was successful, then the .air file should open and Twhirl should install. Follow the on screen instructions and Twhirl should be up and running.
8. By default, Twhirl will install into the 'Accessories' menu in Ubuntu.