TechSpot posted a guide on how to resize Windows 7's taskbar thumbnail preview

Although Windows 7's revamped taskbar has largely received praise, it's not perfect. In fact, it can't be. It's impossible to accommodate every neurotic proclivity -- unless you have the proper utilities, of course.

Adding to our collection of topics on tailoring Windows 7, this week we're looking at the Windows 7 Taskbar Thumbnail Customizer. As its name implies, the software lets you tweak the thumbnail previews displayed when hovering over a taskbar icon. After downloading the program, simply extract and run it, no installation is required. You should see a window with a number of adjustable sliders for the thumbnail size, spacing, margins, and delay time.

Resize Windows 7s Taskbar Thumbnail Preview