the voltage to the reader is supplied by an external power source and its the correct voltage, If I take the reader and connect a DB9 pin on it, connect to my pc and present my tag to it, it will spit out the correct values in HyperTerminal.
I think there is still some misunderstanding - the external power source does not directly relate to RS-232 (serial) line signal levels. If the reader works when directly plugged into PC (DB9), this means it uses ±10-15 V signals and that is why it does not work with Netduino, which requires 0/3.3..5V ("TTL UART").
Technical note: RS-232 transceivers usually have voltage boosting 'charge pumps' to convert supply voltage, e.g. 5V to +10..15V and -10..-15V required by the transmission line.
On a side note, If I purchase this reader (Link below) Can I connect this directly to netduino and read my tag code ?
http://netram.co.za/...odule-uart.html
Most likely yes, there is "UART TTL interface" in the feature list.