I don't quite feel like producing an article right now... what you're asking for should be easy to find on Google. If you have a question slightly more specific, I'll be glad to answer though.
First, you shouldn't compare the X1900XT to a 7900GT, the X1900 kills the 7900GT. If you're going to compare a X1900XT or an nVidia card, compare it to the 7900GTX.