Nevermind. It was a bad dmg file. I allowed it to verify the dmg before running, and got a codec overrun error.

Downloaded it a second time. This time it said invalid checksum, but ignored that and tried again. This time it passed validation for that particular package, but later on in the install (near the end of the install I may add... I was so close!) another package failed validation. I'm downloading it for the THIRD time off Apple's website and hopefully this one will not be corrupt in some fashion.

Unless a download ends prematurely, you never get these corruption errors with exe files. Is this some "dmg" specific issue?