I don't own a PS3 but I have tried using NTSC games in a PAL PS2. The system will output them in PAL60, so your TV needs to support that. I'm using a composite cable without any issues, so it really looks like a PAL60 issue rather than the type of cable you're using.
Of course, things may be completely different for a PS3, but I assume that they're kinda similar 🙂