If you look at your code:
GUICreate("Test WIndow", 655, 500, -1, -1, BitOR($WS_MINIMIZEBOX, $WS_MAXIMIZEBOX, $WS_GROUP, $WS_CAPTION, $WS_POPUP, $WS_SYSMENU))
Global $testlist = GUICtrlCreateList("", 350, 10, 300, 450)
Dim $input
$Input is a global variable so you should not use Dim to declare it. It's not really good programming practice to even use Dim as it has weird scope rules, either use local or global. We just went over this on AIM so shame on you.
I'd answer your question but I think you're trying to run before you can walk!
If you search the forum you'll find examples of both reading from an .ini and using StringFormat, I was just posting in a few threads like that the other day.