Schau mal in der Hilfe hierzu:
[autoit]_GUICtrlListView_GetItemText($hWnd, $iIndex[, $iSubItem = 0])
[/autoit]Und was denkst du, soll:
_GUICtrlListView_GetItemText($hWnd, $iIndex[, $iSubItem = 0]) sein? 
Beispiel:
#include <GuiListView.au3>
#include <GUIConstantsEx.au3>
#include <Array.au3>
#include <ListViewConstants.au3>
Opt('MustDeclareVars', 1)
[/autoit] [autoit][/autoit] [autoit]Example()
[/autoit] [autoit][/autoit] [autoit]Func Example()
Local $listview, $button, $item1, $item2, $item3, $input1, $msg, $Sel, $hListView
GUICreate("listview items", 220, 250, 100, 200)
[/autoit] [autoit][/autoit] [autoit]$listview = GUICtrlCreateListView("Spalte1|Spalte2|Spalte3 ", 10, 10, 200, 150, $LVS_SINGLESEL);,$LVS_SORTDESCENDING)
$hListView = GUICtrlGetHandle($listview)
$button = GUICtrlCreateButton("Value?", 75, 170, 70, 20)
GUICtrlCreateListViewItem("item2|col22|col23", $listview)
GUICtrlCreateListViewItem("item1|col12|col13", $listview)
GUICtrlCreateListViewItem("item3|col32|col33", $listview)
GUISetState()
Do
$msg = GUIGetMsg()
Select
Case $msg = $button
$Sel = _GUICtrlListView_GetSelectedIndices($hListView)
MsgBox(0, "ListViewItem", "Col1: " & _GUICtrlListView_GetItemText($hListView, $Sel, 0) & @CRLF _
& "Col2: " & _GUICtrlListView_GetItemText($hListView, $Sel, 1) & @CRLF _
& "Col3: " & _GUICtrlListView_GetItemText($hListView, $Sel, 2) & @CRLF)
EndSelect
Until $msg = $GUI_EVENT_CLOSE
EndFunc ;==>Example
Edit: Hier nochmal ein Beispiel mit WM_NOTIFY:
#include <GUIConstantsEx.au3>
#include <ListViewConstants.au3>
#include <StructureConstants.au3>
#include <WindowsConstants.au3>
#include <GuiListView.au3>
Opt('MustDeclareVars', 1)
[/autoit] [autoit][/autoit] [autoit]Global $listview, $button, $item1, $item2, $item3, $input1, $msg, $Sel, $hListView
GUIRegisterMsg($WM_NOTIFY, "WM_NOTIFY")
GUICreate("listview items", 220, 250, 100, 200)
$listview = GUICtrlCreateListView("Spalte1|Spalte2|Spalte3 ", 10, 10, 200, 150);,$LVS_SORTDESCENDING)
$hListView = GUICtrlGetHandle($listview)
GUICtrlCreateListViewItem("item1|col12|col13", $listview)
GUICtrlCreateListViewItem("item2|col22|col23", $listview)
GUICtrlCreateListViewItem("item3|col32|col33", $listview)
GUISetState()
Do
Until GUIGetMsg() = $GUI_EVENT_CLOSE
Func WM_NOTIFY($hWnd, $iMsg, $iwParam, $ilParam)
#forceref $hWnd, $iMsg, $iwParam
Local $hWndFrom, $iIDFrom, $iCode, $tNMHDR, $hWndListView, $tInfo
;~ Local $tBuffer
$hWndListView = $hListView
If Not IsHWnd($hListView) Then $hWndListView = GUICtrlGetHandle($hListView)
$tNMHDR = DllStructCreate($tagNMHDR, $ilParam)
$hWndFrom = HWnd(DllStructGetData($tNMHDR, "hWndFrom"))
$iIDFrom = DllStructGetData($tNMHDR, "IDFrom")
$iCode = DllStructGetData($tNMHDR, "Code")
Switch $hWndFrom
Case $hWndListView
Switch $iCode
Case $NM_DBLCLK, $NM_CLICK
$tInfo = DllStructCreate($tagNMITEMACTIVATE, $ilParam)
MsgBox(0, "ListViewItem", "Eintrag: " & DllStructGetData($tInfo, "Index") + 1 & @CRLF _
& "Spalte: " & DllStructGetData($tInfo, "SubItem") + 1 & @CRLF _
& "Spaltentext: " & _GUICtrlListView_GetItemText($hListView, DllStructGetData($tInfo, "Index"), DllStructGetData($tInfo, "SubItem")) & @CRLF)
EndSwitch
EndSwitch
Return $GUI_RUNDEFMSG
EndFunc ;==>WM_NOTIFY
Den Button habe ich entfernt. Linksklick auf das ListView wählt aus.
Da wir dein Hauptprogramm nicht kennen, können wir auch nicht viel helfen. 
Edit: In meinem 1. Beispiel ist ein Include überflüssig. Beim 2. ist alles korrekt.
