By "task bar" I am assuming that you mean the top panel. Were you running
GNOME 2.x or Unity with the previous version? If it was GNOME then I have
bad news for you. It is no longer available in the repositories. Ubuntu
switched to GNOME 3 from GNOME 2 with 11.10. That means no more GNOME as
you know it. The top panel is gone and is replaced with a side Launcher and
a Dash button at the top of the Launcher. No more menus.

The new interface is called Unity which is a shell that runs on top of
GNOME 3. The decision to kill GNOME 2 was made by GNOME and not Ubuntu.
They have their own Shell which unfortunately for you does not work or look
like the old one either.

You have options. All of these alternatives are in the repositories and can
be installed WITHOUT re-installing.
maketecheasier.com/.../27

There is also a faux GNOME that gives a top panel on top of the GNOME 3
base. It looks a bit like the old one with menus, but does not work the
same. It has a GNOME 3 base. It is the GNOME Shell session fallback.

to get GNOME shell install gnome-shell.
to get GNOME Fallback install gnome-session-fallback
to get KDE install kubuntu-desktop
to get XFCE install xubuntu-desktop
to get LXDE install lubuntu-desktop
alternatively you could install kde, afce or lxde respectively. This
removes the Canonical branding.

See: http://www.youtube.com/watch?v=zABkGcaWv6M

Other choices are to re-install. You could install Ubuntu 11.04 (you cannot
rollback, unfortunately), 10.04 (which has GNOME 2 and is good with support
until April 2013) or Linux Mint which does not provide upgrades, but offers
a more traditional layout. However, note that The upcoming Mint does away
with GNOME 2 as well and will offer a similar faux GNOME experience as the
GNOME Session Fallback mentioned above and for that you do not need to
re-install. The big difference is that GNOME's fallback has the menu and
panel at the top and Mint puts it at the bottom like Windows.

You have more options still. You can stick with Unity and try to learn it.
You can add things to Unity or GNOME Shell. There are many extensions and
add-ons such as bottom panels (Tint2) and even a menu button. Most require
adding PPAs to your sources list but they provide good instructions on this
and then you install them through the Software Centre or Synaptic.

A useful resource for anyone who wants to tweak GNOME Shell or Unity in
11.10:
www.webupd8.org/.../...fter-installing-ubuntu.html