Hi Julie,

Normally, the easiest way of implementing single instance application is
using global named mutex. The principle of this approach leverages the fact
that mutex kernel object can have a global name associated with it.
Multiple processes can see the same registered name. So if the first
process has created the name, the second instance(process)'s creation will
fail.

.Net has the build-in support for the named mutex, so it is easy to use
this approach in .Net:
"Ensuring that only a single instance of a .NET application is running"
http://www.ai.uga.edu/mc/SingleInstance.html

The remind requirement is passing the command line argument of the second
instance to the first running instance. You can leverage any type of
inter-process communication technologies to get this done, such as named
pipe, socket, Remoting etc.. Sure, since .Net only has native support for
.Net Remoting, it is recommended to use it. The article below demonstrated
this:
"Single Instance Application, Passing Command Line Arguments"
http://www.codeproject.com/cs/threads/SingletonApp.asp

Hope it helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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