The ethernet connection should work out of the box. I have installed
hundreds of distros and never had to install an ethernet driver in Linux. I
have had to do this in Windows though.

The instructions I gave were for wireless because you did not say how you
connected and the fact that you could not connect suggested a wireless
problem. If it was ethernet it would have connected in my experience.

The internet network manager is in the system tray. Hover over the icons to
find it. If you right-click on it it will give a different menu than if you
left click on it. This is where you initially set up your connection by
either Editing or managing connections (not sure of the exact wording as it
changes and I am in Lucid KDE and not Karmic GNOME). Setting up a connection
won't help you if you don't have a driver yet.

In Windows you would feed the computer a disk supplied by your manufacturer.
In Linux it is either supplied by the kernel or the repositories. This is
why you need to find out if the driver is installed. If the kernel has the
driver then you just have to go ahead with the second part and set up your
connection. Skip down.

If need to use the Windows driver or you need a driver from Hardware drivers
then you need an internet connection to get the driver or application that
allows you to use your Windows driver. You will have to use your ethernet
cable to hook up temporarily to get what you need. Once connected then you
open go to Hardware Drivers. If one is available then it will proceed to
download it. However, if there isn't one then you may have to try Synaptic
to install the application to use your Windows driver. You should install
two packages in Synaptic ndiswrapper-common and ndisgtk. The second package
is a GUI that makes installing the Windows driver a breeze. If you do not
have an internet connection ndiswrapper is on the installation Live CD. You
can get it from there instead of the repos.

Afterwards you will need your Windows driver disk. Run ndisgtk from the menu
or press Alt-F2 and type ndisgtk and press enter. Follow the instructions.
You will likely need to re-boot to use it since it loads earlier in the boot
process before you get to the GUI. I am not sure on this as I have only used
it once and that was awhile ago.

A third option is to go to Dell and see if they offer a driver for Ubuntu.
They sell select models of Ubuntu computers.

Once you have a driver installed then you need to set up your connection.
You do this in Windows too. You go to the network manager in the system
tray. Edit or manage the connection. Make sure wireless box is checked to
connect first. Set up a new wireless connection in the wireless tab. You
will need the info that you had to set up wireless on your router. You will
only need to know the SSID which is the name that you gave to your wireless
network (it shows up when you scan for it), your security type (Whether it
is WPA Personal, WEP etc) and the security key. The rest of the time accept
the defaults. If you have any unusual connection info then you may have to
adjust this, such as if you use static IP. Also there is a check box that
automatically connects you wirelessly when you boot up. Make sure it is
checked or you will have to connect manually each time you boot up.

Perhaps a Dell user or networking guru (I am not. I connect by ethernet most
of the time) can provide more info. Anyone takers?