To clarify this issue: The message "There is an error with your serial number as entered ... error code 18" has nothing to do with video cards or video drivers. The error indicates that the startup code is unable to find a file. When troubleshooting the issue you'll want to focus on other software that involves files access and I/O, such as access control software, anti-virus, disk compression or optimization software, etc.
You might try:
1) Re-installing to a different drive or directory (i.e. try C:\Program Files\Matrix Games\... instead of the default "C:\Matrix Games\...."
2) Check your security for the install folder (via the Windows Explorer, right click the folder and choose "Properties", then go to the "Security" tab). Make sure you have (under whatever account you're logged in on) permission to Modify, Read & execute, List folder contents, Read, and Write in that folder and all sub-folders.
I will see if I can find out the status of this issue from Greg's successor. Possibly it got lost in the transition.