Actually if you put your cursor over the divider between each section then a double-edged arrow will appear which means you can drag it in either of those directions. See
drag partition & resize of interface (click on link) & you'll see what I mean. The arrows that Fabion pointed out are for showing just one section in the entire window (eg: show just search results, etc.) A more specific example is below. There's two other possible solutions. One is to delete the LW Prefs folder & sometimes this problem is solved by closing & re-opening LW.
