There are reports already that Fable 2 will come out on PC end of February 2009. Not officially announced, but my bet is pretty safe.
Still I don't know why they even making PC ports. 360 games ported to PC don't tend to sell that well imo:
Gears 1 flopped on PC
Mass Effect was average on PC
Halo 1 and 2 flopped on PC
Fable 1 did average on PC
Fable 2 will probably be average as well...
Seems to me that people who are really interested in those games already have a 360 version of them. Perhaps the cost to port them to PC is like really minimal?