This doesn't need to be a real time solution, but are there some log files or system messages that could be read to identify periods of time where someone was connected via RDP to a Windows 7 machine?
I'm building a watchdog script for a computer which will be deployed in a remote place and would like to add this metric to a daily status update.
If you look at the Event viewer and the tab Security you can find when people login/logout there. Not sure if it gets logged if the session is just disconnected though.
This seems to be a Python library to access the event log: http://timgolden.me.uk/python/winsys/event_logs.html#module-event_logs
Disclaimer: I'm looking at a Windows 2003 server and not Windows 7, so mileage might vary :)