Simplest method I can think of is to monitor key stroke frequency. For instance in action shooters we know that the main keys that are used are (w,a,s,d) and the arrow keys. For given that you could watch the frequency see if the key W or Up arrow is being held down for a long time, i.e. 1 second, and then bring up a nag screen.

Or you could see when the OpenGL or DirectX libaries are being used, there must be a method of doing that?

I'd imagine this will take a lot of research to achieve and cost some to, as the games are either gonna need to be found and purchased to see what processes run on game time, or massive search of the internet.

Is there a way to "hook" the gamespy thing as well, as that gets installed with nearly every game I can think of? prehaps bounce it to 127.0.0.1 and there might be data contained in there?

i2c