I've found a nice little app, hope you will like it! 
Windows 7 Taskbar Thumbnail Customizer will allow you to customize Windows 7 taskbar thumbnail previews in detail. You can change the size of the thumbnail, its spacing, top, bottom, left, right margins and mouse delay time too!
Windows 7 Taskbar Thumbnail Customizer Home Page | The Windows Club
Windows 7 Taskbar Thumbnail Customizer will allow you to customize Windows 7 taskbar thumbnail previews in detail. You can change the size of the thumbnail, its spacing, top, bottom, left, right margins and mouse delay time too!
Windows 7 Taskbar Thumbnail Customizer Home Page | The Windows Club
My Computer
- Computer Manufacturer/Model Number
- home made
- OS
- Windows 7 RTM x64
- CPU
- AMD X2 5000+
- Motherboard
- Asrock
- Memory
- 4GB
- Graphics Card(s)
- Nvidia 9400GT
- Sound Card
- onboard 6Ch
- Monitor(s) Displays
- Medion 22" + HannSpree 22"
- Screen Resolution
- 1680X1050 + 1920X1080
- Hard Drives
- Intel SSD 80GB
WD 1.5 TB
WD 1 TB
Samsung 1TB X 3
- PSU
- noname
- Case
- noname
- Cooling
- Zalman
- Keyboard
- DeLUX multimedia keyboard
- Mouse
- Microsoft
- Internet Speed
- 25MB/s
