Hi Folks,
At the request of a couple of users I have written a basic guide to serial communication in c#. It takes the form of a turtorial where I walk you through setting up a simple application to send and receive data over serial from the Arduino.
http://www.gaffertapeandcableties.co.uk/electronics/simple-serial-with-c/
If you already have a background in c# programming and only want to know how the send and receive elements work then just skip to step 4 of the guide.
Hope this helps.