there's the swap trick. I'm not sure of the details because ive never done it, but it basically involves starting the playstation with a legit game in it, and then quickly swapping the disc at a certain point in the boot process
You mean play copy disc on PS1 without mod chip ?, Yes it can be done, I have done it myself and very tricky to do and take a lot of practise http://www.youtube.com/watch?v=IW3cFEOLNWA ISO's are images of the disc that are ran from a PC emulator I would rather play them on emulators these days like ePSXe v1.8.0 are pSX v1.13 , with a standard USB joypad.
Very gritty to try, but fun I pulled the middle black cog out of the center of my old PS, had to glue it back in trying the methard at the time ;D