EDIT: An updated tutorial with different printing and washing techniques can be found here: http://www.polishthestars.com/2011/09/techniques-for-printing-on-fabric.html
I first saw the tutorial for printing on fabric here. It is so easy! You start with some spray adhesive:
Spray it onto a piece of cardstock and place your fabric on top, being sure to get out as many bubbles as possible. (I recommend spraying the adhesive outside.)
Then cut down the fabric so that it is the exact same size as your cardstock.
Place it in your printer with the fabric facing whichever side gets the ink.
You now have printed fabric!
Just peel it off of the cardstock.
And you are ready to use your new printed fabric!