in the root of your sdcard have a folder called PSXISOS , you can put your PSX images there (cue/bin or iso). I cant remember where the bios files go, but if you search for 'wiisx wiki' in google, that page will explain all, as well as show you the complete folder structure.
You may also want to search for the 'wiisx compatibility matrix' on wiki, that gives you a list of all PSX games tested on the emulator, and any tips/settings/notes to get each game running optimally. Its been a while, but I played FF7 on WiiSX and I remember it ran fine.
Good Luck with it .. :>