Here's the source for ONCE - a windows utility that starts other apps and then will switch to that instance rather than starting a new instance. The command line for ONCE is 
ONCE ininame 
where ininame is the name of a standard windows ini file with the following information
   [PARAMETERS]
   AppFileName=file name of app to run - including path
   AppTitle= the name to appear on the Title bar*
   WorkingDir=path for working directory*
   IconFile=file name and path of icon file*
   IconNumber=index of icon in icon file 0=first*

* the last four parameters are only required for DOS apps.
  Windows apps ignore them.

This program is useful for new users and in our company's case where two instances of a DOS comm app crash and it is critical to avoid starting the second instance.

