Can't say I've played the PSX version.. if your referring to Final Fantasy Chronicles. It was basically a direct port I believe, just with added in Anime cutscenes - got some flak for having slow loading times and what not though:

http://au.gamespot.com/ps/rpg/finalf...-review&page=2

If, however, your referring to Chrono Cross.. then yes it is different, it's the prequel.