Preventing Multiple Instance

I need to prevent the user from opening multiple instance of an application? If an instance is already running and if the user clicks on the exe icon i need to shift focus on the application which was opened?

Am able to display a MessageBox if there is already an instance running like:

Code:

---

if(System.Diagnostics.Process.GetProcessesByName(System.Diagnostics.Process.GetCurrentProcess().ProcessName).GetUpperBound(0)>=1)
{
MessageBox.Show("An Instance of the application is already open.","Press Inventory Management",MessageBoxButtons.OK,MessageBoxIcon.Information); 
this.Close();
}

---

Help me out?

I got the answer:
http://www.codeproject.com/csharp/oneProcessOnly.asp

but this uses: System.Runtime.InteropServices

Is there anyway of doing it without System.Runtime.InteropServices as this will not be as efficent as an inbuilt .NET class something like System.Application...or Ssytem.Applications..where one can enumerate all the Applications running?