Emacs in Ubuntu Terminal: Meta key opens menus

You should be able to disable menu activation by unchecking the correspoding box in the shortcut dialog under Edit.

Right-click on the emulator window to make the menubar visible, if it is not visible.

As I am a debian user I'm not sure if this solution still works in ubuntu at least in version 2.30.2 of gnome-terminal it was possible to change it this way.

Unfortunately the gnome guys seem to to be uninventing the ui so fast, that I'm not sure if it is still possible.

In ubuntu 12.04 for gnome terminal:

Go to Edit -> Keyboard shortcuts... and uncheck Enable menu access keys (such as Alt-F to open the File menu).