It was just a rumor earlier this week but now it's official. During Konami's E3 2009 press conference this week they indeed confirmed that Metal Gear Solid Rising will be released for the PC as well as the Xbox 360 and PS3 consoles. Other than the fact that the game will feature Raiden as the main character no other info on the title was announced (no release date either.
Konami rarely releases PC games. It's last such game was a port of Silent Hill Homecoming and that game was only released via digital download from Steam. The upcoming Konami game based on the Saw horror movie franchise will be released for the PC this fall.