We keep getting lots of requests for serial port support in the .NET Framework.  We are planning to have it in the next release of the .NET Framework.  You can goto http://www.gotdotnet.com/team/clr/bcl/demos/demos.aspx, and check out the code in either the 'serial support demo', or the 'space invaders!' demo. These showcase the serial support we've introduced for the next release

 

Have fun!