I had to download it from different servers (US, NL or Germany) before I was able to launch Blender. On the first try from one of the servers for download, I was not able to launch it after double clicking it. If your Mac has over 16MB for VRAM and have problems with launch, it may be worthwhile to download from the different server. I was able to install it on my iBook and Ti PB. I also downloaded onto my Fujitsu Tablet PC (when I open it on my Tablet PC, Blender pops up one of those Terminal-looking window briefly before the full launch). I am trying to learn this program; I have one of their training book. I have been still stuck at the first or second chapter as I am totally new at 3D program.