The phenomenon that is Guitar Hero 2 is set to hit the Xbox 360 on April 3rd 2007.
It has been announced that the Xbox 360 version will contain 10 new songs that were not found in the Playstation 2 version. However here is song that was not announced, officially anyway. According to Xbox Official Magazine March 2007 issue, the Xbox 360 version could get a awesomely unique downloadable song that is none other than Steve Vai's electric guitar version of "Halo Mjolnir Theme Song".
source: Xbox Official Magazine March 2007