Tried the FF7 special game fix in the video plugin already? If it's FF8 or 9 you're having a problem with, then perhaps playing with the framebuffer settings will work.
Better still, Kane at NGEmu has a configuration guide specifically for the Final Fantasy games.
Ooh, great call there, Allnatural. I was going to be needing a site like this before long, seeing as how I just ripped my entire PSX game collection to PC over the weekend to play games on epsxe.