The Finder acts up funny every once in a while for me too, showing the wrong icon for some files. Goes away after a reboot. About the hdz extension - is there any 3 character extension that's not taken already, at all? One of reasons why IMHO the .3 extension file typing should finally die and why I hate Apple for adopting that on OS X (just because everyone jumps off the bridge, you don't have to do it too).