Thank you all for your comments.
It´s a pitty that I won´t have the time to develop it further.

But maybe it is a help for some of you. I can´t make a tutorial, just because
I know exactly as much as you about DirectX.
Take a look at the file "meshes.c" to get an idea on how to do it.
I failed when it comes to create a good uv mapping.
So basically the faces are streched simply over their skins.
Also I´m afraid that the meshes are not closed and that they contain a lot of
unnecessary vertices.

So it´s really quick and dirty and more or less a bad example.
All information comes here from the forum, mainly from ventilator and firoball
in some bug-threads. I´ve adapted their short examples and then I´ve played around with them. It´s quite fun.

Do a forum search for "LPD3DXMESH" and you´ll find them. Also, the msdn-site is a good friend.

I´m glad that the game actually makes you some fun.
I´m no big tower defense fan, but I´ve loved C&C with its tesla towers.