Cross application communication/control

Hello.
I would like to know how to get started with writing applications wich control or get data from other (3rd party) applications. For instance, lets say I would like to get the temperature data from SpeedFan, or how to send a message to an open MSN chat window and press the Send button. Some of the applications I would want to control, dont use WinApi GUI, but use Qt. I tried searching on google but couldnt find even half decent material on that topic... Please help me out.