I have added support for ToolTips for the HUD.
All you need to do to use them is to start the MouseStopManager like this:
InputSystem.getInstance().getMouse().startMouseStopManager();
Since this starts a separate Thread, this is not enabled by default.
You can simply set the ToolTip for a Widget by doing:
myWidget.setToolTip( "blah" );
The ToolTips are created through a ToolTipFactory, which is attached to the HUD instance. See the setToolTipFactory() method. By default the HUD keeps an instance of DefaultToolTipFactory, which creates Labels with light-yellow background and a sunken-bevel-border.
If you want ToolTips with a different look-and-feel, you just have to create you own ToolTipFactory implementation and attach it to the HUD.
Marvin