Direct 3D 7.0 Immediate Mode when i push a 3d mesh far away while animating(or even translating it on the timekey) from the viewport camera the polygons begin to disappear.this makes it look real crappy this doesen''t happen in case of microsoft''s meshes(heli.x). even two boxes close to each other reveal this artifact. should i use the w-buffer?? Please give me the reason to this problem and how do i fix it????

I''m not sure exactly what your problem is. Is it that polygons seem to poke through each other when rendered at a distance, or do they simply vanish?

If they vanish then I would say that you have set the far clipping plane to close to the camera.

If they poke through, then you have z-buffer aliasing, this can be somewhat remedied by shrinking the distance between near and far clipping plane.

The w-buffer can also lessen depthaliasing at far distances but at the same time it increases the aliasing a near distances. You will have to compare w-buffer against z-buffer to see which is better. Keep in mind that w-buffer is not widely supported by hardware accelerators yet.