It really shouldn't matter because your display is under 24". If it was larger, say 27 or 30" then you would want a Mini Display Port to Dual link DVI Adapter and DVI-D cable.
Looks like your Dell E207WFP monitor supports both DVI and VGA input.
For a DVI monitor connection, use the Apple supplied HDMI to DVI Adapter and a good DVI cable.
For a VGA only monitor, you would need to buy a > Mini DisplayPort to VGA Adapter - Apple Store (U.S.), connect that to the Thunderbolt/MiniDisplay Port use a good VGA cable.