How to show a window that acts like a popup menu?

When window A is show, I want to show another none-modal popup window B, but: - I don't want window A to become inactive due to window B becomes the front window; - I want that when window B is focused, I pull down a combo box control on window A with one click (generally you have to click twice, one for moving the focus to window A and the second for pulling down the combo box); As you can see, the window B that I want is something like a more usable popup window like a popup menu (which is less a obstacle than a general none-modal window when you want it to get away by clicking on any other part of the parent window). Am I clear on my question? Thank you.