1. http://xbox-scene.com/versions.php to find out your xbox version
Also I was looking at this post by Frosty. It looks like he released a softmod for a dual-boot VGA that does not require a flashed bios.
Sounds like a lot of work to just to get 480p from the Xbox.
Im going to add to the "go with component" advice by mentioning that IIRC there were some VGA monitors that it simply did not work with. I believe it had issues either with synch on green or possibly non-synch on green VGA monitors.