Ubuntu has a number of terminal emulators that you can use, including xterm and the gnome terminal. If you install the kubuntu desktop package you can also use konsole under ubuntu.

Setting the default terminal emulator is easy by using the update-alternatives command. Open a terminal window and type in the following command:

sudo update-alternatives --config x-terminal-emulator

You’ll see something similar to the following, although you may not see as many options on your system:

There are 7 alternatives which provide `x-terminal-emulator’.

Selection Alternative
1 /usr/bin/xterm
2 /usr/bin/uxterm
3 /usr/bin/koi8rxterm
4 /usr/bin/lxterm
*+ 5 /usr/bin/gnome-terminal.wrapper
6 /usr/bin/konsole
7 /usr/bin/xfce4-terminal.wrapper

Press enter to keep the default[*], or type selection number:

Just type in the number of the selection and hit enter. Now when you launch the terminal via the menu item, or by typing in x-terminal-emulator at the command line, you will see the correct window pop up.