(These steps assume you already have a version of Eclipse installed under /opt.)
Like this:
$ wget http://ftp.osuosl.org/pub/eclipse/technology/epp/downloads/release/ganymede/R/eclipse-jee-ganymede-linux-gtk.tar.gz
$ tar xzvf eclipse-jee-ganymede-linux-gtk.tar.gz
$ cd /opt
$ sudo mv eclipse eclipse-europa
$ sudo mv ~/eclipse .
You should now be able to launch Eclipse Ganymede using the same shortcuts or scripts as before.