To make your karmic koala look like  lucid lynx is easy. Here are the links to debian files you need to download to make it work ,desktop  items and icons . Download the files and double click on it to install it.Then, to select the themes, select System> Preferences> Appearance and in the flap Subject, For Ambiance or Radiance . Choose your theme and have fun. If you need to try something different take a look at how to make your ubuntu linux look like mac os .