The only official word on Alan Wake is Spring 2010 Xbox 360 and Games for Windows according to wikipedia.
The only thing I see on Wikipedia is this: Alan Wake is billed as a "psychological action thriller" and is due for release on Xbox 360 in Spring 2010, with a Windows release possibly following aftewards.
Which is accurate because Microsoft hasn't officially announced anything regarding the PC version. No mention of it whatsoever at E3. Now Remedy states that they are focusing exclusively on the 360 version. That doesn't bode well for the PC version.