Right click a tab, choose Tab Settings from the menu, in the config dialog, click Positioning > Show dock as drawer. You can use Mouseover activation, or use the Hotspots setting to activate the dock.

Oh ... I guess I missed the point. You want the tabs hidden as well.......... that would be counter productive to having a tab in the first place wouldn't it? You can shrink the tab in the Size & Appearance settings, or as Stephen suggests make completely transparent tabs.

The transparency level is set within the tab images themselves, you can adjust that by opening the tab images in either Photoshop or PSP....unfortunately there is only two tab images for each set of tabs, one for normal tab and one for the Selected tab. Until, if ever, OD+ supports a third state....mouseover....there's not much else that can be done (With a mouseover image you could make the normal and Selected tabs transparent and have the mouseover image visible....giving the appearance that the tabs were always hidden) Another problem is the text on the tabs, It just has one color setting that is used by both the normal tab and the Selected tab and there is no transparency with the text.