Apparently it's one of these: http://focus.ti.com/docs/prod/folders/print/tsc2200.html
GPIO 5 goes 1 from 1 to 0 a lot when screen is touched and stylus moved around.
the code from the TI appnote slaa169 is mis-matched with the appnote tsc2200. pay special attention to the TwoWordThingyRead function, if you don't do EXACTLY what it does, you cannot possibly hope to get a valid response from the tsc2200.
the tsc2200 also deals with keys and battery monitoring.
Additional information: http://focus.ti.com/lit/an/slaa197/slaa197.pdf