Help with LCD Monitor... PLEASE

Hi

I have a question or a problem, my monitor supports a 1440 x 900 resolution, but the resolution that the Xbox 360 accepts is 1280 x 720, I can change to that resolution in my monitor, but my question is: what happens if I leave the monitor to 1280 x 768 which is another resolution which I can change too, or what happens if I leave it in 1440 x 900?

Please, help me out, today I'm buying the VGA cable and I'm playing in it today

Thanks

One last thing, any of these resolutions are better than SD right?