To adjust windows 7 taskbar previews
1.Open Registry editor.To open windows 7 Registry editor Click Windows 7 start button and type REGEDIT and click REGEDIT program.
2.Click HKEY_CURRENT_USER folder and go to
software>Microsoft>Windows>CurrentVersion>Explorer>Taskband.
3.Right-click in the task pane on your right side, select New and click DWORD (32 bit) value.
4.Rename to MinThumbSizePx
5.Double-click MinThumbSizePx and select Decimal.And then set any value more than 350 to enlarge the taskbar previews