Cool, didn't know google earth would do a gpx, when i click on the d/l link it just displayed the code so I didn't mess with it.
Jsun, if your still having troubles, give these instructions a go!
To run GPSBabel, you need to unzip the files, I just did this onto my desktop. Then run the GPSBabelGUI exe file. In the program under Input Section, choose your gdb file by clicking the button all the way to the right side of the section, the icon is a page. Next in the Output section do the same thing for your save location, this time the button is a page with a disk. Make sure to choose the save as type to be "Google Earth (Keyhole) Markup Language (.kml)".
Once that is done, hit the let's go button in the bottom right and it should say your file has been created (or something along those lines.