Time for a bump...

I decided to go a different road, something unrelated to this, but the same idea.
I have this external program and I want to make another topmost form above it.
Any pressed keys or mouse events that this topmost screen obtains are redirected to the underlying program, thereby keeping track of what is going on.

For this I need a 100% transparent form, 99% would either make the program underneath lighter or darker, or worse, coloured. On my OS (Windows 7 32 bit) I have no problems with this; I can simply click on the transparent window. But I fear that on other machines the OS will click through the form (and click on the program below). A colorkey could be used as well, but the same clickable rule must count there.

I see I have to trick the OS into believing a form is present at the location, whilst drawing a completely transparent form. Anyone has any idea of how to accomplish this? I tried some regular commands like setting layered to true, they do not work out.