I have downloaded a deb package of skype. But i don't know how to install it in my ubuntu 11.04 system. when i double click the package it shows me an install button with Skype in "Ubuntu Software Center". When i click install, it starts to download the package again. Can't i install the skype when i already have the package. Someone please suggest...
It is most likely downloading dependencies. That's why it's generally better to install things online: dependency resolution happens for you. You can download individual debs for any of the packages you need, but as soon as you try to install one which depends on a package which is not currently installed, the package manager will automatically try to download and install what you need from a repository.
The easiest way to get a full list of missing dependencies is to install the package in dry-run mode, which does nothing, but tells you what would have been done if it were not run in dry-run mode. For instance,
dpkg --dry-run -i skype.deb
If you want to install offline, you'll need to first get a deb of each dependency. Put them all in the same directory, and then from that directory do
dpkg -i *.deb
to install them all.
Skype seems to need these dependencies:
These are the things Aptitude tried to install on my Lubuntu (plain Lubuntu, only Aptitude and Alien installed.)
You could try to get every dependence as a .deb and then install the dependencies first.