Have you checked the 'How Do I Customize the Taskbar?' link at the bottom of the Taskbar Menu?
By the way, are you using the old Taskbar Context Menu or the new Tasbar Context Menu? Windows 7 introduced a redesigned right-click Taskbar Context Menu for the Taskbar icons which includes new features, although the old Context Menu from previous versions of Windows is still there. If you're using the old menu, you might not be getting all your available options.
To show the NEW Context Menu - Click and drag upwards an application's Taskbar icon to show the new Taskbar Context Menu using a fade in effect (similar to right-clicking the application's Taskbar icon).
To show the OLD Classic Context Menu – Hit Shift + right-click an application's icon in the Taskbar or Start Menu to show the Classic Windows Context Menu. To get the same result, you can also right-click an application's live Thumbnail.