Have you tried System/Administration/Synaptic_Package_Manager?
You can set up local repositories in Synaptic also.
Synaptic tells me GDebi is installed....
Is this the Applications/Add_Remove link?
Because when I hit this link, this is what I see:
Failed to check for installed and available applications
This is a major failure of your software management system. Please check for broken packages with synaptic, check the file permissions and correctness of the file '/etc/apt/sources.list' and reload the software information with: 'sudo apt-get update' and 'sudo apt-get install -f'.
I never go though this avenue, I use synaptic where you have to input your super user password to use.