With the GPS connected your probes probably do not generate enough electrical noise to make garbage come through the serial connection.
Actually I had my arduino outputing "hello world" then a delay of 1 sec, via its serial port (com 5), and the gps outputting it's data on it's seril port (COM4).
i had two terminal windows open at the same time, one watching each com port. when i probed the gps PL2303 recieve pad , i noticed i started geting hello world, on both terminals, and no data from the gps at all. I then figured out the GPS chipset feeding the PL2303 was only 3.3v, and since the arduino is 5v, at the same bit rate, it was overideing the gps output. make the arduino run the blink sketch, with no serial output, reprobed and wha la! works.
if i can read it, then arduino can read it right? Now gotta build a parsing script, to decrypt lat and long, so i can show it on my LCD.
gotta go google how to do that.
thanks to all who helped