3D Engine in Pure VB.net

Hi Friends,
This is long time after I am here on my blog. This is about the 3D stuff that I recently learnt and tried to implement in Vb.net 2010.
This project does't use any of directX, OpenGl or XNA, It is completely written in pure VB.net. Actually I learned VB.net through this project.I made this project just to learn VB.net 2010 so it is not written in professional way. So please do not bother about that, Just look at what it can do.


Screenshot:


Source code Link:
[url="http://www.mediafire.com/download.php?p5zp4cp7gkmso3g"]


I could successfully implement:
1. z order sorting
2. z buffer(beta)
3. lights(beta)
4. cartesian, polar, parametric plot
5. gradient coloring


I could't implement
1. Polygon intersection(hidden surface removal for intersecting objects) ,BSP Tree
2. Shading models
3. Menus settings are not working since I first wanted to resolve following problem and then working on this project from scratch again. Menus just show what I am keeping in mind for its further development


The biggest problem in further development 
How to deal with Intersecting objects? I have some options
1. Use ZBuffer: It works fine , but it seems to be slow and it can draw only solid colored objects, how to draw wireframe model using it. 
2. BSP tree: I dont know how to implement it
3. RayTracing: i can use it but it seems that it will also be slow.
4. use XNA/ directx/OpenGL as Engine(but I don't want that)