I want to intercept messages that are being sent to a window in a different process. What is the best way to do this? I can't see the messages when I use the WH_GETMESSAGE hook, and I'm not sure if I can subclass across processes? Any help would be much appreciated.
You need to inject your own code into the process that owns the windows you wish to intercept messages from. Fortunately,
SetWindowsHookEx() makes this fairly easy, although you may have a bit of trouble at first if you've only used it for in-process hooking up to now.
I can recommend two excellent articles on the subject: