To add the calendar feed from calendar.gsu.edu to the All-in-One Event Calendar on your site you need to get the calendar feed. This tutorial will quickly explain how to do this.
Navigate to calendar.gsu.edu
Click the Subscribe icon
In the dialog box choose iCalendar Dynamic Feed and copy the WebCal iCal URL
Now that you have the .ics feed, follow the directions on the article Import Calendar Feeds for the All-in-One Event Calendar starting at the 'Add the feed to your calendar' section.