I purchased a JVC GZ-MG330 this week and spent all afternoon trying to open the video on my IMAC 10.4.11 after downloading as per the manual. Thanks to this forum I followed a link to JVC UK and downloaded a video and all you have to do is once you follow the instructions to your EVERIO_HDD logo on the desktop (don't open a new folder as they suggest)- with camera still connected open IMOVIE 08 and up pops your video with the prompt to IMPORT ALL - select that and away you go - they download into IMOVIE. If it doesn't work with the prompt, go to FILE - IMPORT FROM CAMERA prompt- this should work.
thanks to this great forum. My first visit - thanks guys and hope it helps.