You would use ShellExecute to open the program(I feel as if I said this before)
And for editing the textbox and button pressing you can use SendMessage or PostMessage to send/post messages to the program. Of course you need the window handle. Get the window handle using FindWindow.
In this case you should use FindWindowEx since you're looking for child windows.
I'm sorry I can't give examples it's like 1:30 and i'm tired.