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First you have to add medibuntu repository.
you can choose one of the following methods for adding medibuntu repository
Open a terminal and type
$ sudo wget http://www.medibuntu.org/sources.list.d/hardy.list -O /etc/apt/sources.list.d/medibuntu.list
$ sudo apt-get update
$ sudo apt-get --yes -q --allow-unauthenticated install medibuntu-keyring
$ sudo apt-get -q update
OR
# gksu gedit /etc/apt/sources.list
and add the line
deb http://packages.medibuntu.org/ karmic free non-free
OR
Open System -->Administration-->Synaptic Package Manager and then Settings --> Repositories -->Other Software --> ADD --> deb http://packages.medibuntu.org/ karmic free non-free
After Adding Medibuntu
$ sudo apt-get install skype
Now Your skype is ready for use
$ skype
If you have a any difficulty you can directly download the deb file and install
Download the deb file for skype from here
now double click on the deb file
or
open a terminal and type
$ sudo dpkg -i skype-debian_2.0.0.72-1_i386.deb