Cross-fading transforms a shape from one form to another, with OpenOffice.org handling all of the intermediate transitions. The result is a new group of objects including the two end points and the intermediate steps.
To carry out a cross-fade, select both objects (hold the Shift key while selecting each object in turn) and then choose Edit > Cross-fading The following dialog appears.
On the dialog choose the number of increments (transition steps). You probably want to have Cross-fade attributes and Same orientation both checked. The end result is shown below.