I haven't played around much with a PC webcam but here's what you can do about the GPS mouse. What you need to do (if it is possible with your GPS) is to configure it so it outputs only NMEA $RMC sentences. There should be some kind of program that comes with the unit that allows you to do this. Once this is done, connect to the GPS via your serial port using HyperTerm (after setting the proper baud rate, bits, etc. If working properly, you should see $RMC sentences fill up the screen. When you are ready, choose the option to capture the data to a file in HyperTerm. When you are done wiht your outing, close the file.
Google GPS Visualizer which has a utility to convert your file to a .KMZ file which is what Google Earth likes. Once converted, just double-click on the .KMZ file and you got your path displayed. Good luck!
BTW, what brand of GPS mouse are you using?