When your system doesn't output too much data, or in order to signal some special events an audio output can do the job. Most laptops come with a Sound Blaster compatible sound card and a lot of PC-104 cards are sold with such a sound card on board or you should buy a sound module. The next step is to redirect your text output to a text_to_speak program.
As a lot of input is done using emacs, it seems to be a good idea to use Emacsspeak