MACROMEDIA FLASH 8-COMPONENTS LANGUAGE Reference page 146

The label is set below the check box. The check box and label are centered
"bottom"
horizontally and vertically.
The label is placed below the check box. The check box and label are centered
"top"
horizontally and vertically.
You can change the bounding area of a component while authoring by using the
Transform command or at runtime using the
information, see "Customizing the CheckBox component" on page
Example
The following example sets the placement of the label to the left of the check box:
checkBox_mc.labelPlacement = "left";
The following example uses ActionScript to create check box instances. The check box
instance has its label and labelPlacement properties set within the method
right_ch
"UIObject.createClassObject()" on page
and labelPlacement properties set in separate declarations. Drag the CheckBox component
from the Components panel to the current document's library (so the component appears in
your library, but not on the Stage). Then add the following ActionScript to the first frame of
the main timeline:
this.createClassObject(mx.controls.CheckBox, "right_ch", 1, {label:"Right",
labelPlacement:"right"});
right_ch.move(10, 10);
this.createClassObject(mx.controls.CheckBox, "left_ch", 2);
left_ch.label= "Left";
left_ch.labelPlacement = "left";
left_ch.move(10, 30);
See also
CheckBox.label
144 CheckBox component
UIObject.setSize()
1362. The check box instance
property. For more
132.
has its label
left_ch