The program works by utilizing the SQLDataSources API of the ODBC32.DLL.

private Declare Function SQLDataSources Lib "ODBC32.DLL" _
   (byval henv&, byval fDirection%, byval szDSN$, byval cbDSNMax%, _
   pcbDSN%, byval szDescription$, byval cbDescriptionMax%, _
   pcbDescription%) as Integer
'
private Declare Function SQLAllocEnv% Lib "ODBC32.DLL" (env&)
'
Const SQL_SUCCESS as Long = 0
Const SQL_FETCH_NEXT as Long = 1
'
Sub GetDSNsAndDrivers()
    Dim i as Integer
    Dim sDSNItem as string * 1024
    Dim sDRVItem as string * 1024
    Dim sDSN as string
    Dim sDRV as string
    Dim iDSNLen as Integer
    Dim iDRVLen as Integer
    Dim lHenv as Long         'handle to the environment

    on error resume next
    cboDSNList.AddItem "(None)"

    'get the DSNs
    If SQLAllocEnv(lHenv) <> -1 then
        Do Until i <> SQL_SUCCESS
            sDSNItem = Space$(1024)
            sDRVItem = Space$(1024)
            i = SQLDataSources(lHenv, SQL_FETCH_NEXT, sDSNItem, 1024, _
                iDSNLen, sDRVItem, 1024, iDRVLen)
            sDSN = Left$(sDSNItem, iDSNLen)
            sDRV = Left$(sDRVItem, iDRVLen)

            If sDSN <> Space(iDSNLen) then
                cboDSNList.AddItem sDSN
                cboDrivers.AddItem sDRV   '---optional - driver
                                          '--- value returned
            End If
        Loop
    End If
    'remove the dups
    If cboDSNList.ListCount > 0 then
        With cboDrivers
            If .ListCount > 1 then
                i = 0
                While i < .ListCount
                    If .List(i) = .List(i + 1) then
                        .RemoveItem (i)
                    else
                        i = i + 1
                    End If
                Wend
            End If
        End With
    End If
    cboDSNList.ListIndex = 0
End Sub
'