Windows 7 has thumbnail preview feature. Taskbar Thumbnail Preview displays small thumbnail preview of opened window on your taskbar when you hover your mouse on taskbar icons. Many users have started loving taskbar thumbnail preview of windows 7.
We can access this feature in Windows XP but with the Alt+Tab combination. There is a small application available from Microsoft for this. This PowerToy enhances the existing Alt + Tab application switching mechanism of Windows XP. It provides a thumbnail preview of windows in the task list and is compliant with the new Windows XP visual style. You use this just as you do the existing Alt + Tab mechanism. Press and hold the Alt key and then press the Tab key to cycle through the running applications. When the desired application is highlighted release the Alt key. You can move backwards through the task list by pressing and holding the Shift and Alt key and then pressing the Tab key.