yeah it is a bummer, I was looking forward to using the mouse and keyboard on that game. Reading through PC gamer, August 2007; page 104.
by Gary Whitta
"Asta La VISTA"
Skip about half way through the fluff..

"And yet, we're expected to be so hungry for this game that not only will we buy it, but we'll upgrade our entire operating system, too. Microsoft seems to think that the Halo brand can be a "system-seller" on the PC the way it has been on consoles. UH, no. People aren't going to jack up their systems with an expensive unwieldy, resource-hogging, and largely unproven OS just to play this game, and anyone who thinks so has been spending too much time hanging out with the other stoners on Xbox live."
Skip the rest of the fluff..