I get the message below when trying to install PAL on Windows7?

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Windows Installer

This installation package could not be opened.  Verify that the package exists and that you can access it, or contact the application vendor to verify that this is a valid Windows Installer package.

- Did you download the latest install from CodePlex? 
- Does the same install work on a different machine? (If you don't have a different machine you can try, then you can try running it on your XP mode VM that comes with Windows 7)
- Are you trying to run the install from a network drive or UNC path or is it on your local disk?
- Is the install located in a folder which your Windows account doesn't have permissions to?
- What happens when you do: "Run as Administrator"? 
- Could any anti-virus be blocking the install from getting executed?

I would assume the install package installs the necessary pre-requisite programs instead of just shutting down like this, but perhaps you can check the pre-requisites to see if installing them separately help.

Just my two cents, here...

Good luck!  

Most likely you are on a 32-bit version of Windows 7. The default package for PAL is the 64-bit version. Go to the Downloads tab of the PAL project and look the latest version of PAL zip file with x86 (32-bit) in the name, then install that one. Please keep in mind that the 32-bit version of PAL is limited to 2 GB of virtual address space (this is true for nearly all 32-bit applications) regardless of the physical RAM or paging files. PAL is very memory and processor intensive, so you might need to upgrade to a 64-bit version of Windows assuming your computer hardware can support it. 64-bit applications get 8 TB of virtual address space. Virtual address space is a "fake" memory environment allowing applications to "think" they have a lot of memory.