Semi-transparent form using alpha-PNG background

[James Arnold]

I am trying to use a semi transparent PNG as the form background,
allowing you to see through certain parts. The intention is similar to
a skinnable form like launchy, with semi-transparent pixels (not
just .MakeTransparent or Form.Opacity). Also similar to the Adobe
splash screens which the feather and drop shadow.

By overriding the OnPaint method and manually drawing a PNG onto the
form background I can achieve this effect, but it does not update when
the form is moved or content under the form changes. Invalidating the
form simply repaints the drop shadow and any other semi-transparent
pixels over the existing ones, causing those parts to darken.

An example: http://www.launchy.net/images/screenshot_sheep.jpg (the
vista-like border).

Thanks in advance,
James.