Question: In order to take a screenshot of a specific window, I need to place a white colored TForm behind that window. What Windows API could I use to change the z-order of my window and place it correctly ?

Answer: 
Try the [`SetWindowPos()`](http://msdn.microsoft.com/en-us/library/ms633545%28VS.85%29.aspx) function.
On Delphi you can use`SendToBack` method, `.Top` and `.Left` properties.

```
form1.Top := ...;
form1.Left := ...;
form1.SendToBack;

```

> 
> procedure SendToBack;
> 
> 
> Description
> 
> 
> Use SendToBack to change the order of
>  overlapping controls or forms.
> 
> 
> The order in which controls stack on
>  top of each other (also called the Z
>  order) depends on the order the
>  controls are placed on the form. For
>  example, if you put a label and an
>  image on a form so that one is on top
>  of the other, the one that was placed
>  first on the form becomes the one on
>  the bottom. Because both the label and
>  the image are non-windowed controls,
>  they "stack" as you would expect them
>  to. Call the SendToBack method for the
>  top object to move it below the other
>  object.
> 
> 
> The stacking order of two windowed
>  controls is the same as the stacking
>  of two non-windowed controls. For
>  example, if you put a memo on a form,
>  then put a check box on top of it, the
>  check box remains on top. Calling
>  SendToBack for the check box makes the
>  memo appear on top.
> 
> 
> The stacking order of windowed and
>  non-windowed controls cannot be
>  mingled. For example, if you put a
>  memo, a windowed control, on a form,
>  and then put a label, a non-windowed
>  control, on top of it, the label
>  disappears behind the memo. Windowed
>  controls always stack on top of
>  non-windowed controls. In this
>  example, calling the SendToBack method
>  of the memo does nothing, the label
>  remains behind the memo.
> 
> 
> If the control has the input focus
>  when the SendToBack method executes,
>  it loses the input focus.
> 
> 
> 

(Edit: [WinSnap](http://www.ntwind.com/software/winsnap.html) is a very good utility for taking and editing screenshots)