How to get application's Windows taskbar button to show progress of progress bar
It can be easily accomplished using the ITaskList3 COM Interface.
For using it in Delphi check the following link:Fun with the Windows 7 Taskbar
Also Check this link for complete article describing the features provided by ITaskList3 Windows 7: How to display progress bar on taskbar icon?
You can also use TTaskbarListProgress component from the TaskbarListComponents open sourced component pack. Released under the dwywbdbu license.