Let me first say I have a Mac, and I'm running a program called DVD copy, which rips and burns dvds very quickly. I love the program. Thing is, when I rip them to my computer, I save the file to the desktop, burn it, and then delete the file from my desktop. For some reason, my harddrive space keeps decreasing and I can't figure out why. I burnt around 10 dvds yesterday, and started out with 25 GB of free harddrive space. Now, i'm down to 13. Are these files somehow hiding themselves on my computer? And where would they be?
Ripping, processing and burning DVD's, especially 10 at a time, is bad news for your system with regards to fragmentation and it quickly loses track of how much free space is available. I STRONGLY recommend you invest in an external HD for your DVD needs, they're pretty cheap, will save wear to your main HD, stop the fragmentation problems you're experiencing, and give you somewhere to back up important work too.
Forgot to add that to sort out the free space problem you're experiencing you'll need to run a disk utility to fix the symtptoms of fragmentation you're experiencing. I recommend you do this from an external HD, by booting up from it and run TechToolPro. Carry on as you are and you run the risk of generating bad data blocks on your HD, which means they could be lost forever :OS.
I am not familiar with Mac as I use Windows XP. That being said--there may be a place that is similar that your computer is saving those files even though they were delete. IE. I run Norton Systemworks. Even though I delete a movie backup file and empty the recycle bin. The file is retained in the Norton Protected recycle bin. That one has to be emptied also to get rid of them. You may have something that is doing the same thing. Hope this helps.
Also see Macfixit.com for saving files on your desktop. It's a very bad place to work from. Better to save things on your HD proper. Hope you've bought an external HD in the meantime anyway.