Good lord the Access 2007 help is appalling, isn't it. I've never been able to find anything in office help since 2002...
Anyway, the code you are looking for is
the value of the listbox is the value of the bound column in the currently selected row (at the risk of guessing, if you have a multiselect list with more than 1 item selected you probably get a comma-separated list of the selected items). If you have a multi-column listbox and want to use a value other than the bound column (although why you'd do that is beyond me ) you'd need
txtS.Value = lstS.Value
where columnindex is the zero-based index of the column you're interested in. That example only works for non-multiselect lists though: for multiselects you'd need something like
txtS.Value = lstS.List(lstS.ListIndex, columnindex)
But that's probably enough showing off from me for tonight
Dim result as String, i as Integer
For i = 0 to lstS.ListCount - 1
If lstS.Selected(i) result = result & lstS.List(i, columnindex) & ", "
txtS.Value = result