Do you have your Ubuntu CD/DVD, from which you installed the thing in the first place?
You can start with it. The CD itself already houses a ton of programs that you can install on your system. If you have one, just put it in your CD/DVD drive and open up your Synaptic package manager (from the menu: System -> Maintenance -> Synaptic Package Manager... Sorry for possible inaccuracies, I use a Finnish language version myself, so I don't exactly remember what these things are in English!).
In Synaptic, you should see a list of all the available programs on the right side. On the left side you have a small window where you can categorize available programs in different ways (the first option: "Groups", is the most useful one, because it lists programs in categories like "Science", "Office", "Games" and so on).
If you click on a program on the right window, you should see a description of it below. If you want to install the program, just double-click it and press the button "Execute" (orsomethinglikethat) in the menu bar at the top of the Synaptic window.
If you already double-clicked a program but decide not to install it after all, or if you want to remove a program, just right-click the program in question in the right side window. Then you get a menu with choices like "Delete The Mark" (which ticks off the "chosen" mark),"Mark for Deletion" (which marks an already installed program for deletion).
You can choose several programs like this. After you have made your choices, just hit that "Execute" button on the top menu bar. There is also an "Update" button, which updates the program package list, but this is useful only if you have an internet connection.
Programs on CD/DVD are of course bound to be older versions, but still useful.