Originally posted by ShivaBlizzard8
To my knowledge, they are exactly the same game - its just that once the game reached a certain level of popularity and sold a certain number of copies, it was re-released as a "greatest hit" with a signifigant price reduction. Kind of like a record going platnium or something to that effect. It's a promotional tool more than anything else.
In some countries, they ARE re-released as 'Platinum' titles rather than being labelled 'Greatest Hits'. The packaging and the discs look a little different, but the content is identical. The Platinum release of FFVII, however, came with an interesting demo of FFVIII.