In the "Startup Applications Preferences" window of the Ubuntu "Control Center", you need to do the following:
This will open an "Add Startup Program" window with three input fields.
You can fill in a name and a comment, they speak for themselves. The command field is the important one. You could write this:
/usr/bin/gnome-terminal -e top
This line of text will be executed after X has started and right about when you see the "Ubuntu desktop" appearing. It will start a
gnome-terminal and in it exectute the
top command. The
-e option causes this, because it stands for "execute the argument of this option inside the terminal".
If you like, you can also change the size and position of the terminal window. For that you use the
--geometry option of the
gnome-terminal command to specify this behavior.
man page (manual) of
gnome-terminal for more details:
Or a nice introduction here: