There should be a video mode select button on either the projector or the remote. On my projector it is called "Souce"
When i use a xbox cable (the original one with yellow, red, and white only), i plug it into the projector and select RGB mode and hit the source button until it shows.
you wont be sending a HD signal unless you use a component cable so it doesn't matter that it doesn't support it.
You could try connecting a dvd player and seeing if that works. If one works, the xbox should be hooked up the same way.