Installing Debian packages
Since Ubuntu is based on Debian, it is usually quite easy to install such Debian .deb packages which are not included in standard Ubuntu repositories. This can be done both from command line or using graphical tools.
To install
sudo dpkg -i packagename.deb
and to remove
sudo dpkg -r packagename
or reconfigure
sudo dpkg -reconfigure packagename
You can also use gdebi from command line or a graphical version
gdebi-gtk
TeknoMagus 
Hi,
I’m extremely new for the ubuntu. Recently installed the old version of ubuntu 9.10. I dunno how to install the downloaded softares. I’m trying for it for the past two days. Can i save the .deb downloaded softwares in the desktop and give the command. I gave “sudo apt-get install” command, it didn’t install. It said the software not fount..