Although this may not help with any Macs, I have had some issues getting my roommate's television, also at 1366x768, to properly work with my Dell OptiPlex GX270. It would either be 1024x768, centered, or 800x600, for whatever reason, stretched.
The odd-but-it-worked solution, at least how I thought of it at the time, was to update the graphics drivers.
All of that having been said, I'm going to put in another good word for SwitchRes, you can manually set a lot of things, you can use it to overdrive single-scan displays (although that's not too reccomended) or hook up an LCD and run it at native resolution through an otherwise disagreeable VGA adapter or mac > vga cable, that was designed (or pinned, or whatever) for 640X480@60Hz, and nothing else.
The odd-but-it-worked solution, at least how I thought of it at the time, was to update the graphics drivers.
All of that having been said, I'm going to put in another good word for SwitchRes, you can manually set a lot of things, you can use it to overdrive single-scan displays (although that's not too reccomended) or hook up an LCD and run it at native resolution through an otherwise disagreeable VGA adapter or mac > vga cable, that was designed (or pinned, or whatever) for 640X480@60Hz, and nothing else.