Relatively new convert to mac. 20" aluminum iMac. 4GB of ram. Its not my primary machine, just my video editing machine. Most of the time I have a macbook. I went to my machine today, and it said I have no HD space on the boot HD. All my video files are on external HD's.. I emptied the trash, and it cleared up about 80GB, which is rapidly declining. Something is writing massive amounts of info to my HD, and I have no clue what it is. Help. Don't even know where to start to troubleshoot.