I'm not sure exactly what I need, but after tooling around on ebay I've found the following:
- 12v 12" linear actuator, which will push/pull the window.
- 12v switching power supply with sufficient grunt to run the actuator and a Pi.
- 12v to 5v USB adapter (to power the Pi!)
I already have a motor controller for the Pi, I won it in a raffle years ago and just never got around to using it. This will drive the actuator forward or backward to open or close the window.
I need to find a temperature sensor I can use outside (I've posted a question, if anyone's got any bright ideas!), which I'll get two of and use one inside too.