I think if you're looking for help with DirectX and the Win32 api you're on the wrong forum.
Alternatively using a "proper" GUI api will save you pain in the long run - eventually you *will* need the more advanced controls like scroll panes, tables, trees etc. and you could waste a lot of time writing your own versions of those. The Swing tutorial
is pretty good iirc (although I'd skip the bit on Netbeans myself).
Or you could save yourself even more time and use an existing map editor. There's lots around, like <shameless plug>Analog
</shameless plug>, or Tiled