Can I connect an RFID reader to the ICSP header? I am connecting an RFID reader to my Arduino mega.  The directions that I have found say that I need to use pins 50-53.  I also noticed that the ICSP header contains (what looks like) a secondary connection to these pins: 

http://arduino.cc/en/Reference/SPI

Can I connect my RFID reader to the ICSP header:
Yes you can. However the SS isn't present on that header. You can however use any pin you want for SS (if the library you use supports it, that is)