Cheap, easy, crappy way of doing this:
Get on a mac, open terminal. You can customize the terminal window to have a black background with green text. Then use a screen capture program to capture yourself typing into that window. You can use some unix command (slips my mind at the moment) to change the prompt. You can even perform an SSH login to another mac where you customize the welcome message etc.
Sorry, that's a pretty crappy way of doing it, but I guess it works better than some....