Disappearing Hard Drive Space - Help!

Hopefully I can explain this accurately - Recently I was trying to create an iDVD disk image file to my main hard drive. The iDVD project file was on my external hard drive. I have a 40GB eMac with about 10GB free space, so I thought I could create my 7GB iDVD file on my main drive with no problem - I thought wrong. Just as the task was about complete, it errored out saying I was out of hard drive space, and it was correct, I was at 0. Then iDVD froze on me, I force quit, threw my half complete disk image (@4GB) away, but am now missing about 6GB of space which I cannot account for. I restarted several times, did a search under the project name, ran Disk First Aid off my install disk and still cannot find this mysterious 6GB file to trash! I threw the project file away as well from my external (which had plenty of room) just to be safe. VERY frustrating, because it seems simple, hopefully someone can help!

Thanks, Dave