This blog corresponds to the scripting guy column with the same title.   I am posting the script for doing the same with PowerShell

   1: $processes = get-wmiobject -query "Select * from win32_process where name = 'notepad.exe'"
   2:  
   3: if ($processes.count -le  2 )
   4: {
   5:   return
   6: }
   7:  
   8: $datetarget = [DateTime]::Now
   9:  
  10: foreach ($process in  $processes)
  11: {
  12:    $dateholder =  $process.CreationDate
  13:    $dateholder =  $process.ConvertToDateTime($dateholder)
  14:  
  15:    if ( $dateholder -le  $datetarget)
  16:    {
  17:     $processid =   $process.ProcessID
  18:         $datetarget  =  $dateholder
  19:    }
  20:  
  21: }
  22:  
  23:  
  24: $processes = get-wmiobject -query " select * from win32_process where name='notepad.exe' AND processID <> $processid"
  25:  
  26: foreach ($process in $processes)
  27: {
  28:    $process.Terminate()
  29: }