To install Skype on Lubuntu 13.04, you must activate the "Canonical's partner" repository as follows:
1. Access sources.list
sudo /etc/apt/sources.list
2. Uncomment the lines that contain the repository removing the almuadillas (#)
deb http://extras.ubuntu.com/ubuntu raring main deb-src http://extras.ubuntu.com/ubuntu raring main
If you don't have the repository then add it, copying the two previous lines
3 To update
sudo apt-get update
4. Install Skype in the usual way through the Ubuntu Software Center or via terminal with the following command
sudo apt-get install skype
It could also be done through a ppa, but so if it can be done in a safer way, right?
I'm working on a script that does all this automatically. When I have it I will post it here on desde linux