I want to play the PSX version of Tales of Eternia but the game consists of three separate discs. Is there a way to burn all three discs on one dvd and still make it work correctly?
No. The Playstation cannot read DVDs, so even if you did get it to burn right, it wouldn't work. Just burn them onto three CD-R.
1 game-one cd disc only. EMulators/playstations can't read multi boot games anyway, unless they made an app to make it work like this (like with gamecube games).