If you used just "apt-get install eclipse" then you'll probably face some troubles trying to install new software.

 

The problem is that the package, once installed, does not include the eclipse update sites in the installation, so eclipse couldn't get additional packages that are needed by other packages (like Maven)...

 

Add this sites to your installation sites!

 

Galileo:
http://download.eclipse.org/releases/galileo

EPP Packages:

http://download.eclipse.org/technology/epp/packages/galileo

Eclipse Project Updates
http://download.eclipse.org/eclipse/updates/3.5