Here are a couple of screenshots using the NXT-G block for the RFID sensor. Here's what you're looking at:
1. The RFID block uses port 3 by default.
2. Data ports going from top to bottom: Port, Command, Transponder # In, Inverse Comparison, Transponder # Out, Yes/No, Raw Value 0, Raw Value 1, Raw Value 2, Raw Value 3, Raw Value 4, Error
3. Transponder # In and Transponder # Out are actually TEXT data types, not Number because they are given in Hexidecimal
4. Config Panel - left side: Port # on top, Operation drop-down menu has options for Single Read, Continous Read, and Stop. The Compare drop-down can do equal and not-equal. Clicking the Current Transponder button puts that transponders # in the text box right above it.
5. The Live Update checkbox on the far left will display the current Transponder # that is placed in front of the sensor.
6. Config Panel - right side: Clicking the Read buttons provides basic information on the sensor - right now, the Type is RFID, mfr is CODATEX, and version is v1.0. The other Read button provides the sensor's serial #. (Not sure yet what value this information will provide other than knowing the version # of the sensor's firmware.)
In one screenshot, no transponder has been detected. The other shows the Live Update grabbing the # and I also clicked the Current Transponder button to lock it into the text box.