Hideo Kojima has explained that he will not be directing development of Metal Gear Solid Rising, but will instead concentrate on the newly announced PSP game.
This year's E3 conference brought the announcement of two Metal Gear Solid games; Metal Gear Solid Rising, and Metal Gear Solid: Peace Walker. The former will star Raiden as its main protagonist and is in development for the Xbox 360 and PlayStation 3 (as confirmed by Famitsu magazine) and the latter will star Snake and is in development for the PSP.
The series' creator, Hideo Kojima, has explained in a Famitsu interview that he's actually only fully involved with the PSP game.