oil pressure sender install

hello,
i am having problems with my oil pressure light in my '02 Jetta GLS 1.8T. i'm going to replace the oil pressure sender/sensor as a first solution. the problem is, no one i have talked to knows where it is located. does anyone know where the oil pressure sender is located so i can replace it? also, does the oil need drained before I replace the sensor?

thanks,
randy