This is an appropriate place to post such a question, but I don't have any sure fire fixes for you.
Since you are using a Mac system, you might try removing the preferences file for the older version of FileMaker and see if that makes a difference.
Moving the plist for that version of Filemaker from the HD > Users > youruser > Library > Preferences with FMP closed may help.
Changing the screen resolution to a smaller size, opening FMP 6 and testing may help. If it does, close FMP and then reset screen resolution.
This assumes there is only one screen attached to the computer and has not had another attached in the recent past.
This is a little more involved
Screen resolution was already at it's finest, so couldn't reset it to show more. But the Pref file was the solution. Thanks both of you.