Converting a game from PAL to NTSC is possible but finding the patches for it can be time consuming.... Will your mod chip NOT let you boot PAL games? Or is your TV not a multi-system tv. If you CAN boot PAL games BUT don't have a multi-system tv you can pick up converter boxes that will convert the PS2 signals from PAL to NTSC....
Take a look at mrmojorisin76 post. He gave you a good starting point for finding your patches....