How can you tell if a computer has an nForce2 easily? I know I can check if the nVidia drivers got installed by checking for files like nvmctl.nmu or something similar, but I do not want to detect nForce1 or nForce3.

Look in the "System Devices" section of Device Manager.

Or maybe you can use the DeviceID. I doubt if that's been done before...

Use Microsoft's tool "Devcon" to do this.

link to Devcon's KB article