Hi. I suppose the installation didn't go very well. Did realplayer work?
Well, you should write some information about your distro and/or at least what desktop environment(GNOME? KDE? XFCE? etc) you use.
Anyway, if you open new window, and "minimize" it, you can probably get it back by pressing ALT+TAB, which switches between opened windows.
If you use GNOME:
Can you open gnome-terminal? If you can then you still have access to programs, so if your panel is gone, you could type
and you would have your panel back. You would then have to save your user session.
If you don't use GNOME, can't open a terminal, your GUI isn't of any use:
Press CTRL+ALT+F1, this will get you to the Linux console. You might have just moved some files around, so looking for them and putting them back would be a good idea. The command line should be enough for this task.
Or, as a desperate solution you could use aptitude or whatever package manager you like from this same command line, and re-install your GUI.