I've searched this topic and found plenty of answers but none of them helped me.

So I've got a 160 gig HD. I know that the actual space is much lower than that (~150). But whenever I add movies and whatnot from iTunes or wherever, I see the space disappear from in the Finder Browser under "xxx Gb available". However, whenever I delete my files, I sometimes only get part of the space back. Sometimes I get none of the space back. And I'm doing this with 100+ meg files so it should definitely be noticeable. I am using Secure Empty Trash to empty my trash bin.

Does anyone know why it won't add the space back to my HD and how to fix it? Thanks.