virtualbox.org

Why can't I see the small screens (Live taskbar previews) in the guest?
Host and Guest: W7 Home Premium

From MS site:

Live taskbar previews
In Windows 7, you can point to a taskbar button to see a live preview of its open windows—including webpages and live video. Move your mouse over a thumbnail to preview the window full screen, and click it to go open the window. You can even close windows and pause video and songs from the thumbnail previews—a big time saver.

Live taskbar previews are available only in the Home Premium, Professional, Ultimate, and Enterprise editions of Windows 7

Guest additions installed (in the guest)? Did you see the 3D and install the wddm drivers?

Yes, I found it in the installation proccess.
In my version (4.1.4) it is still experimental...
Thank you.

Aero is activated?
Aero is working?
What is manufacturer of your graphics adapter?

ATI Mobility Radeon HD 5730 (Deafult LCD)