Download Visual Taskbar Tips for XP
If you see carefully, at above screenshot, you will observe Windows XP tooltop for taskbar items with and without visual detail. You can enable Windows vista style thumbnail tooltip for items minimized in taskbar for Windows XP using Visual Task Tip.
Visual Task Tips is a lightweight shell enhancement utility. It provides thumbnail preview image for each task in the Windows Taskbar, as seen in the Microsoft Windows Vista. Windows XP or Vista (Classic theme) is required to run Visual Task Tips. Its simple, useful and free.