Hmm, RGB? I think it can do 1024x768. Isin't that was the $box uses for high def? Infact, ain't it the only way most consoles work anywho? lol. It's probaby the cheapest method of achieving high def, probably not the best, but definately a good solution, most common for sure.
Anywho, it really depends on your Projector man, check what rez it's capable of. You could always try more, but odds are it wouldn't work. I know if ya plugged from the comp to the tv and go above 512x480 onna S-video cable, it'll work, but it'll be a very bad sight for the eyes.
It's defiantely possible man, lots of people have done it. This hea's a cool pic:
the ONLY way to truly play NS. gg.
Oh, and I'm sure you can buy a s-video to rgb cable, or converter.
I say, just use VGA man. It does high rez, works great. DVI only shows huge improvement on tvs really since no tv's support VGA. RGB ain't any better than VGA anywho.