serial port communication between computer and another hardware device via RS232

Question

I am developing an application in C#.NET , for transferring data between two PC's using RS232 protocol. For communication, i m using "SerialPort" class of "System.IO.Ports" namespace. but now i have a problems in recieveing the data and sending the data. even one major problem is whenever i'll recieve at that time i have to identify the begining of message and ending of message as well as if two messagees are recieveing at thae same time then how to differentiate that messagees. please help me i nthat. i really stuck in that. thank you in advance