Using only one instance of an SDI application

I developed an SDI application that I want the user to launch by clicking on the desired document file from My Computer (on 95/98/NT). Unfortunately, if the user clicks on another document file a new instance of the application is launched. How do I force the operating system to use the first instance of the application instead of launching a new instance?

There are 3 or 4 different ways to do this - look in the misc section of codeguru:

http://codeguru.com/misc/index.shtml

My favorite of the methods there is http://codeguru.com/misc/single_instance3.shtml

Josh