it's a rumorang.
With that caveat out of the way (and stowed safely in a locker somewhere), we'll proceed to relay the rumorang your way: An unnamed Konami rep apparently dropped some knowledge on Xbox Family, whispering that MGS4 would sneak onto the Xbox 360 12 to 14 months after the PS3 version is released (whenever that is). The site also published a lengthy email from Microsoft's John Porcaro basically saying "no comment" which they also suspect may be further proof of the rumor. (Why did he write so much? He's very polite, you know.)
With Konami execs straight up saying that Metal Gear Solid 4 may go to other consoles, and MGS4 producer Ryan Payton saying the game needs to sell a million copies on day one to make the pricey production profitable, it's not like Konami's showing their best poker face either. But that doesn't mean it's not still a rumor which, of course, we don't need to tell you guys.
[Thanks, The Dutch Slayer]