In case you haven't found it, here's the code. (To run this example, put a listbox with the default name List1 on your form, then paste this code into the form.)
Code:
Option Explicit
Private Declare Function SendMessage Lib "user32" _
Alias "SendMessageA" (ByVal hwnd As Long, _
ByVal wMsg As Long, ByVal wParam As Long, _
lParam As Any) As Long
Private Const LB_SETHORIZONTALEXTENT = &H194
Private Sub Form_Load()
List1.AddItem "Line 1"
List1.AddItem "a big Line 2 some text some text"
List1.AddItem "line 2"
List1.AddItem "Line 3"
addHorScrlBarListBox List1
End Sub
Public Sub addHorScrlBarListBox(ByVal refControlListBox As Object)
Dim nRet As Long
Dim nNewWidth As Integer
nNewWidth = 400 ' new width in pixels
nRet = SendMessage(refControlListBox.hwnd, _
LB_SETHORIZONTALEXTENT, nNewWidth, ByVal 0&)
End Sub