How do I make Outlook show the weekday when receiving a meeting invitation?
Outlook uses the system-wide long date format setting, so by changing the long date format in the windows control panel to include 'dddd', outlook will also show the name of the day.
This setting can be found in the Region and Language section of the control panel. In English windows 7 you could search for "Change the date, time, or number format" to find it.