How can I compress a 3 hour video to fit onto a 4.7GB DVD?

Using Adobe Premiere n a Mac. 3 hour video of a class, will be viewed on (Win and Mac) computers, needs to be at least 75% image quality so writing on the board can be read, but everything else can be lower quality. Want to be able to burn it to a single (data) DVD because I need to make 12 copies of the class. Which combination of codecs/settings can I use? Can I use another program to compress it further? Thanks!