Hi Bibang! I'am also having a problem in interfacing my PC to arduino and to my GSM SHIELD. Actually we are, at some point is same in project.
I also made use of RFID reader by RDM, and a database. The overview of my project is; if the RFID card holder swipes its card to the reader, the read RFID code will be sent to the Arduino Mega using a software serial and the arduino will send or echo the read code to the PC database to match the identification and if it matches, the database will sent the needed info. back (accepted by) to the arduino mega to perform another program to command the GSM to send the needed info. to a specific phone no. came from the database and the real-time entering of the student in the campus...
Bibang, if you have already solve your problem would you please post the sketch you use and some sort of procedures...I appreciate If you reply or give any thoughtful ideas to solve my problem..I think 90% of our project is alike.,. 