anyone know details on 125 kHz RFID reader?

Using Arduino Sensors
2

Perhaps the open-source SnifferNano 2.0 would be easier to customize:

Firmware:
http://code.google.com/p/rfidsniffernano/

Schematic:
http://iteadstudio.com/store/images/produce/RFID/SnifferNano/SnifferNanov2.0sch.pdf