Not exactly sure, I have also tried before - depending on what you're planning to do you could use VBScript quite easily:

Set WshShell = WScript.CreateObject("WScript.Shell")
WshShell.Run "notepad"
WScript.Sleep 100
WshShell.AppActivate "Notepad"
WScript.Sleep 500
WshShell.SendKeys "Text Here"

Credit to: InTh33yesOf (for the VBS code)