MacBook 5,2 and External Display

hi.

Just bought a small LED backlit display to run dual displays on my 5,2 MacBook.

The native resolution of the monitor is 1366x768. Using a mini-dvi to vga adapter the external screen is only displaying at 1360x768. I know its only a 6 pixel difference but it doesn't look quite right.

Coming from a unix back ground I would manually set the resoution in the xorg.conf file. Whats the protocal for getting the right resolution in OS X?

That's what I am doing, however the maximum resolution that is showing isn't my monitors native resolution.