Well, I think the 9-pin to 4-pin cable is the best way to go. Get your camera's power adapter out and plug the camera into the wall first. Once the camera's got power, put it into VCR/playback mode. Then also go into the Menus on the camera and also check your manual to make sure you are sending the video signal out through the firewire and not just through the RCA video jacks. I don't know if the GL2 has a control for the Firewire jack, but just double-check that to make sure it's turned on.
Now setup the Mac to recognize the camera. Shut it down completely and plug the firewire cable into the Mac. Make sure your camera hasn't gone to low power/sleep mode. Startup the Macintosh, when you see the desktop appear launch iMovie. Then go to File Menu > Import from Camera. And in that window that pops up it should list your GL2 in addition to the iSight webcam.