If you've come across this problem with unzipping/decompressing zips, you might find this helpful:
I was having a little trouble with unzipping (decompressing) tarred archives under OS 10.5 until today. My first attempt was to just simply double-click on the zip file (i.e., example.tar.gz) and allow the file to unpack, but I ran into an error message which was an "error-1, not permitted to open). I was stumped and thought it might have been the (desktop) location in which I had the file resting in. So I moved the file to root hoping it's containment might be a little more refined, obviously this had nothing to do with it, I got the same error results here also. The file was about 48Gb in size and took quite a while to unpack. Final move was to just simply utilize "Stuffit Expander," and this did the trick.
I took the tarred file and dropped it onto the Stuffit Expander shortcut in my dock and apps launched, it created a receptacle for the files to be unpacked and began unpacking them in the receptacle. Pretty sweet!
P.S. For all you guru's who may have already figured this one out, hats off. Sorry I'm a bit slow getting back to this, despite it's simplicity. 