Need Help In VB & Windows Messaging API

I have an application named Pika Bot. I was wondering how to exit the application by running another instance of the application with a command line argument "Quit". This would come handy when uninstalling the Application. I tried using getmessage & sendmessage API functions to do this, but due to lack of time and knowledge of "Windows Messaging", I failed. Could you peeps please give me a fairly detailed method of doing this?

.NET or plain jane VB?

Its in VB. Although I have managed to do the job using Winsocks.