VB.Net Client Server /Interface

Question

I have an existing Visual Basic Interface program that runs on a Serial Port.  This application connects to another application on a serial port and there is a constant receiving and sending of data between the two applications.  This application connects to several applications on different serial ports at the same time.
Now I need to port this to a TCP/IP based VB.net (VS2008) application.  I would like to have some advice on the following.

1. WinSock or System.Net.Sockets.
2. I need to both receive and send data so how i effectively need to keep the connection to the other applications open all the time till the application is closed. Is this possible?
3. If i use WinSock i can have multiple WinSock controls (1 for each application it will interface to on a dedicated port), If i do it with System.Net.Sockets how can I achieve this?
4. Any sample code for Listening and sending simultaneoulsy either (or both) for Winsock or Sockets would be very helpful.

Regards
Anil