Try using the script available here:
http://www.digidesign.com/index.cfm?navid=3&itemid=33123&downloadid=57180&eid=0

An Alternative is to install Pro Tools one component at a time.

To do so:
1) Run your Pro Tools installer.
2) When you see "Custom Install" stop and uncheck CoreAudio.
3) Click on the right arrow next to "Pro Tools" This will expand the contents.
4) Uncheck DigiRack plug-ins and Free Bomb Factory plug-ins.
5) At this point the only item that should be checked is "Application Files", verify this and hit Continue.
6) The install should complete successfully. Once it does you will need to go back and run the installer again and install the plug-ins and CoreAudio separately.
7) To install the plug-ins separately, follow steps 1, 2 and 3 above.
8) Next, Uncheck Application files and hit continue. Once this process completes run the Pro Tools Installer again.
9) When You get to the "Custom Install" screen, uncheck "Pro Tools" The only thing that should be checked now is CoreAudio.
10) Hit Continue to complete the installation.

If this does not fix the problem, follow these steps:
1) Open your main hard drive on the desktop (commonly named Mac HD)
2) Open "Library" folder, then go to the "Application Support" folder.
3) Drag the "Digidesign" folder out of the "Application Support" folder, and drop it on the desktop.
4) The installer should now work. A new "Digidesign" folder will be created by the installer in /Library/Application Support.