Well Dhampy. THAT IS INCORRECT!
What really went wrong:
Windows Update had did something recently and went out of tolerance for waiting for me to restart the computer, it decided to force a restart on it's own. However, the Halo installer did not finish in time.
So when the computer came back up again (and I was not at the computer) I assumed it was done. There was an icon and everything so naturally I click it and prepare to kick Halo ass. I was greeted with that Window of the invalid key. The reason it returned this was that even though the files were on the hard drive, the installer did not register them in time and had improper hash files. This leads to the online server into flagging the installation as false.
So...using Revo Uninstaller, I discover that the installation process did not make an uninstaller...yeah perfect fitting...a broken program that cannot be uninstalled. So I load the retail CD back into the drive and launch that program to uninstall it. It prompts me to install the program instead. Frustrated, I do this and the installer completes this time. For kicks I try the program once more and Halo CE launches successfully.
The root cause: An incomplete installation.
But...it is still Micrsoft's fault. Windows Update is a core component designed by Microsoft...so burn in hell Microsoft