The Elegant Gnome theme pack does not have a ppa for Ubuntu 11.04. First you need to download it and then install it using some terminal commands.
First download the theme pack from this page. Make sure you download the source package, when download extract the content of the elegant-gnome-1.0.tar.gz file in your Downloads folder. Now open a terminal window (press Alt+F2 and type: gnome-terminal) and copy+paste the following lines:
sudo make install
When install press Alt+F2 and type: elegant-gnome.sh and select Install the pack and click on the OK button. Answer some questions and when the installation is finished log out and back in again and the Elegant Gnome theme pack is installed and ready to be used.
To uninstall the Elegant Gnome theme pack press Alt+F2 and type: elegant-gnome.sh Select Restore the previous settings and click on the OK button. When done log out and back in again.