"apt-get" not finding packages on Terminal

I have been trying to install different packages via Terminal, like laptop-mode-tools, xserver-xorg-input-multitouch or xserver-xorg-input-mtrack, but it never works because I get the error:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package xserver-xorg-input-mtrack

Normally I have been able to install this stuff through the Synaptic Package Manager, but I can't find there the "mtrack" driver.

Any idea why apt-get is not working? I have already run sudo apt-get update several times.

EDIT: I'm running Ubuntu 11.10 in a MacBook Pro with dual boot (Leopard)

Thanks to BlueXrider, JasonD and CS I manage to install the packages I wanted. Apparently it was a problem of sources and package names. This is what I did:

I went to the Ubuntu-x-swat repository here: http://www.ubuntuupdates.org/ppa/ubuntu-x-swat?dist=oneiric

Ran the instructions they provide there:

sudo add-apt-repository ppa:ubuntu-x-swat/x-updates

sudo apt-get update

sudo apt-get install <package name>

And then, instead of the "package header" xf86-input-mtrack (I actually tried, but I still got the "unable to locate" error), installed the package xserver-xorg-input-mtrack

So, as I said before, it must have been a problem between sources and package names. I know have the mtrack driver working (which, again, makes the touchpad tab dissapear from the mouse settings....)

First try searching with apt-cache, to find the exact match on the package you're interested in.

apt-cache search xserver-xorg-input

If the package you need isn't in the list then it's not available in the repositories your system has configured. On my system both laptop-mode-tools and xserver-xorg-input-multitouch are available, but not xserver-xorg-input-mtrack.

Searching google for 'ubuntu mtrack' leads to http://www.ubuntuupdates.org/package/xorg-edgers/natty/main/base/xserver-xorg-input-mtrack

This page show that the package (at least for ubuntu 11.04) is not in the main repository but is available via PPA xorg-edgers http://www.ubuntuupdates.org/ppa/xorg-edgers?dist=natty

Follow the instructions there for enabling the PPA, note the name of the package is xf86-input-mtrack

sudo add-apt-repository ppa:xorg-edgers/ppa 
sudo apt-get update
sudo apt-get install xf86-input-mtrack

I think you are looking for multi-touch pad gesture driver for 11.04, 11.10 and 12.04

The packages are located here http://www.ubuntuupdates.org/pm/xserver-xorg-input-mtrack

## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8844C542

add this to your source.list

deb http://ppa.launchpad.net/xorg-edgers/ppa/ubuntu oneiric main

## Run this command: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8844C542

add this to your source.list

deb-src http://ppa.launchpad.net/xorg-edgers/ppa/ubuntu oneiric main

Managing repositories using command line https://help.ubuntu.com/community/Repositories/CommandLine