I can't picture you scenario exactly, but if you want your app to "listen" for commands while it's running then I reckon the best bang-for-the-buck is the UcpClient class. I've been using UDP over the last few months to let uncoupled apps "talk" to each other. The amount of coded needed is tiny. As I said a few months ago, the UdpClient class is a hidden gem.
Bills solution is for the single instance scenario, if that's what you're after. Greg
