function CreateOutputProgressPage(const ACaption, ADescription: String): TOutputProgressWizardPage;
Creates a wizard page containing static text as well as a progress bar (which is hidden by default).
Unlike the other types of wizard pages, progress pages are not displayed as part of the normal page sequence (note that there is no AfterID parameter). A progress page can only be displayed programmatically by calling its Show method.
Call the Show method to activate and show the page. When you're finished with it, call the Hide method to revert to the previous page.
Always put the Hide call inside the finally part of a try..finally language construct, as demonstrated in CodeDlg.iss. Not calling Hide will result in the wizard being permanently stuck on the progress page.
To set the text on the page, call the SetText method. SetText takes two string parameters: use the first to tell the user what you're doing, and the second to display a file or directory name. Either parameter may be blank.
To display or update the progress bar, call the SetProgress method. SetProgress takes two integer parameters: the first specifies the position of the progress bar (zero-based), and the second specifies the highest possible position. If the second parameter is 0, the progress bar will be hidden.
See CodeDlg.iss for an example.