I'll assume you're using GNOME since the icon that gets added to your post indicating which OS you were using when you posted says 'linuxubuntu' and GNOME is the default desktop environment for Ubuntu.
The anel applet that shows you a list of windows is called 'Window List'. If you right click on the panel you do have, and select 'Add to Panel...' you will see a list of panel applets. Find 'Window List', select it and click Add. That will add a Windows List applet to the panel you do have and you should now be able to see all your windows in there.
If you want to recreate the bottom panel, right click on the panel you do have and select 'New Panel'. A new panel will be added to your Desktop. If the panel doesn't get added at the bottom automatically, right click on it and select 'Properties'.
You could also get back the default panel configuration by deleting your panel configuration. To do this:
- Log out.
- Press ctrl-alt-f1 and log in there.
- Run these commands
$ cd .gconf/apps
$ rm -rf panel
- Now press ctrl-alt--f7
- Log in and your panels should be recreated with the default settings.