Windows 7's window-preview thumbnails pop up when you hold your cursor over a running program in the Taskbar. However, these thumbnails are too small to be of much use. This is especially true on high-resolution monitors, which cram more pixels into a given space and therefore have smaller icons.
Fortunately, we’ve discovered the Windows 7 Taskbar Thumbnail Customizer. This free utility, which was developed by a 12-year-old lets you shrink or enlarge thumbnails to practically any size you want. You don’t have to install anything; just run the program, then drag the Maximum Size slider to alter the thumbnail sizes. Its maximum setting is 512. Click Apply Changes.
This sensible utility offers several other Taskbar adjustments, including spacing, margins and delay time (the wait before the thumbnails actually appear).