PostMessage & sending keystrokes to WoW

Hi there, I've recently gotten into dual-boxing in WoW, I run two copies across a mac and pc and want to write some software to broadcast keystrokes from one to the other. I've gotten as far as intercepting keystrokes and using PostMessage to dump them into other applications, however when I try and do this with WoW rather than, say, notepad it doesn't work. I think this may be something to do with the AttachThreadInput function, but I'm having trouble getting it to work at all.

I'm using Python and the windows API bindings for that, does anyone have any experience with doing this kind of thing? Is there a better way to send keystrokes to WoW, the only other way I could think to do it was using SendInput, but that requires the window to have focus and isn't really what I'm after. I was also thinking it might be that I'm simply sending the messages to the wrong window (I've obtained the window ID by grabbing the ID of the window that a click event on the WoW screen is sent out to, I'm going to try looking at the tree of windows inside WoW to see if sending messages somewhere else might help...)

I'm sure people must've overcome this kind of problem before, so any help would be appreciated :)

Thanks