Re: 1920x1080i ModeLine = "No Valid Mode" for GeForce 6600GT and Pioneer PDP-4270HD
Yep. Sounds like you've got it. Or at least you now know that it's going to work.
I don't know whats going on with the "startx" thing. When you reboot (or whatever) and it doesn't work right what do you get? No display? Corrupt display?
I'm not sure what the "SecurityTypes" option is doing. You might try it with this disabled.