This is what the default dialogs look like:
The main Toolbox is actually quite easy to recreate - it's just the Toolbox dialog (you can create a new one with Ctrl-B or Windows -> New Toolbox if you don't have one), with a Tool Options tab beneath it. Resize the toolbox until a space appears beneath it where you can drop dockable dialogs, then goto Windows -> Dockable Dialogs -> Tool Options, and drag the new dialog's tab into the space.
The other dialog contains four tabs in the top pane: Layers | Channels | Paths | Undo
and three in the bottom pane: Brushes | Patterns | Gradients
Start with the top pane: open the Layers dialog, then open up the Channels/Paths/Undo dialogs (from Windows -> Dockable Dialogs) and drag their tabs in next to the Layers tab.
Then to create the bottom pane, open the Brushes dialog and drag its tab to the very bottom of the dialog window (just above the window border), and the dialog will split into two panes with Brushes at the bottom. Patterns and Gradients can then be opened and dragged into the bottom pane.