Communication between programs?

You want CreateMutex from Kernel32. Lots of documentation about it on the MSDN, of course, but something like this :

Extern "Win32" 
   Function GetLastError:Int() = "GetLastError"
   Function CreateMutex:Int(lpMutexAttributes:Int,bInitialOwner:Int,lpName$z)
End Extern

Const ERROR_ALREADY_EXISTS:Int=183

CreateMutex(0,1,"My Program Instance")

If GetLastError() = ERROR_ALREADY_EXISTS Then
	' PROGRAM IS ALREADY RUNNING - SHUTDOWN
Else
	' PROGRAM IS NOT RUNNING, GO AHEAD
EndIf

That's off the top of my head, so it might not be 100 percent.

EDIT: You may have to make some minor modifications to get the CreateMutex function to link properly, but the site won't let me post them. Sorry about that.