The code is composed of 4 functions:

ClearListBox() - Clears a list box.  It uses a For Next loop and the list box ListCount property to set the Selected property for each item to False.

SelectAllListBox() - Selects all the items in a list box.  It uses a For Next loop and the list box ListCount property to set the Selected property for each item to True.

FillList() - Fills a list box with values parsed from a comma+space delimited string.  It uses Split() to change the string to an array.  Then it uses a For Next loop to work through the array values and compare them to each item value in the list box.  If a match is found, it sets the Selected value of item to True.

BuildDelimList() - Passes back a string of comma+space delimited values from selected values in a list box.  It uses the ItemsSelected collection of the list, combined with the ItemData collection, to concatenate the selected item values together.

The Microsoft Access example is called ListBox Example.mdb.  The functions are located in the code module named basListBox.  When the example opens, the Select Patio form appears.  The left side of the form contains the list box, which uses the Patio table for a record source.  The right side of form contains the text box value, from the Data table, created by selecting values from the list.  View the form code module to see the event code that drives the results. 

basListBox Code:

' basListBox Version 1.0.0
' Copyright © 2009 Extra Mile Data, www.extramiledata.com.
' For questions or issues, please contact support@extramiledata.com.
' Use (at your own risk) and modify freely as long as proper credit is given.

Public Sub ClearListBox(ListCtl As ListBox)
' This procedure clears the ListCtl list box.
On Error GoTo Err_ClearListBox
    Dim intCount As Integer

    ' For each item in the list, deselect it.
    For intCount = 0 To ListCtl.ListCount
        ListCtl.Selected(intCount) = False
    Next intCount

Exit_ClearListBox:
    On Error Resume Next
    Exit Sub
Err_ClearListBox:
    MsgBox Err.Number & " " & Err.Description, vbCritical, "ClearListBox"
    Resume Exit_ClearListBox
End Sub

Public Sub SelectAllListBox(ListCtl As ListBox)
' This procedure selects all the items in the ListCtl list box.
On Error GoTo Err_SelectAllListBox
    Dim intCount As Integer

    ' For each item in the list, select it.
    For intCount = 0 To ListCtl.ListCount
        ListCtl.Selected(intCount) = True
    Next intCount

Exit_SelectAllListBox:
    On Error Resume Next
    Exit Sub
Err_SelectAllListBox:
    MsgBox Err.Number & " " & Err.Description, vbCritical, "SelectAllListBox"
    Resume Exit_SelectAllListBox
End Sub

Public Sub FillList(ListCtl As ListBox, DelimList)
' This procedure fills the ListCtl list box with values parsed from
' a comma+space delimited string of values found in DelimList.
On Error GoTo Err_FillList
    Dim blnFound As Boolean
    Dim strValue As String
    Dim intCount As Integer
    Dim intListItemsCount As Integer
    Dim avarDelim

    ' If there is no list to parse, just exit.
    If IsNull(DelimList) Then
        GoTo Exit_FillList
    End If
   
    ' Create an array of values from DelimList.
    avarDelim = Split(DelimList, ", ")
   
    ' Initialize some other variables.
    intCount = 0

    ' Clear the list box selections.
    ClearListBox ListCtl

    For intCount = 0 To UBound(avarDelim)
        ' Get the array value.
        strValue = avarDelim(intCount)
        ' Initialize the "found" variable and the list item count.
        blnFound = False
        intListItemsCount = 0
        ' Keep looping through the list items until a match with the array
        ' value is found or until there are no more items in the list to
        ' compare to.
        Do
            ' Compare the array value to the list value.
            If StrComp(Trim(ListCtl.ItemData(intListItemsCount)), Trim(strValue)) = 0 Then
                ' If they are a match, then select the item in the list box
                ' and flag that one has been found.
                ListCtl.Selected(intListItemsCount) = True
                blnFound = True
            End If
            ' Increment the list item count.
            intListItemsCount = intListItemsCount + 1
        Loop Until blnFound = True Or intListItemsCount = ListCtl.ListCount
    Next intCount

Exit_FillList:
    On Error Resume Next
    Exit Sub
Err_FillList:
    MsgBox Err.Number & " " & Err.Description, vbCritical, "FillList"
    Resume Exit_FillList
Resume
End Sub

Public Function BuildDelimList(ListCtl As ListBox) As Variant
' This function passes back a string of comma+space delimited values from
' the ListCtl list box.  If there are no selected values in ListCtl,
' it passes back a null.
On Error GoTo Err_BuildDelimList
   
    Dim objItem As Variant
    Dim strTemp As String
    Dim intCount As Integer

    ' Initialize the variable that lets us know whether or not we are
    ' at the first item in the list box.
    intCount = 0

    ' Initialize the variable that will hold the delimited list.
    strTemp = ""

    ' Only proceed if there are items in the list box.
    If ListCtl.ItemsSelected.Count <> 0 Then
        For Each objItem In ListCtl.ItemsSelected
            ' For each item that is selected, add it to the delimited list.
            ' The first one does not need a comma in front of it.
            If intCount = 0 Then
                strTemp = strTemp & ListCtl.ItemData(objItem)
                intCount = intCount + 1
            Else
                strTemp = strTemp & ", " & ListCtl.ItemData(objItem)
                intCount = intCount + 1
            End If
        Next objItem
        BuildDelimList = strTemp
    Else
        BuildDelimList = Null
    End If

Exit_BuildDelimList:
    On Error Resume Next
    Exit Function
Err_BuildDelimList:
    MsgBox Err.Number & " " & Err.Description, vbCritical, "BuildDelimList"
    BuildDelimList = False
    Resume Exit_BuildDelimList

End Function

Download Example: ListBox Example.zip