After a little more poking around, it appears that you are running PHP Version 4.x.x. PowerGallery requires a minimum of 5.2.3.
There is a step in the installer that alerts the user when their PHP Version is inadequate, but in your case, your version of PHP won't even run the code the installer is using.
We're going to look into getting the installer to run on versions of PHP that are less than 5.0.0 so users can at least get a reason why they can't install rather than this ugly parse error.
Thank you for reporting this.