The Windows 7 taskbar displays previews of running programs via some very cool thumbnails. To speed up these thumbnails so that they appear instantly, follow these simple steps:

How to Speed up Taskbar Thumbnail Preview

1. Click on start and type regedit at search bar

2. Navigate to following key in left pan of registry editor

HKEY_CURRENT_USER\Control Panel\Mouse

3. Now locate MouseHoverTime key in right pan of registry editor

4. Doublick on MouseHoverTime or right click modify and change value from 400 to any value less then 100 (400 is milliseconds) lower the value faster the thumbnail preview.

5. Click ok and close regedit widow.

Now check taskbar thumbnail preview by hovering mouse on taskbar icon and it should open faster.

source: blogsdna.com