I recently had cause to draw an ellipse in CB. At one time (2008) there was an ellipse plugin, but I don't see it on the plugins page. However it's pretty simple to do in CB itself.
1) Draw a circle whose diameter is the major axis length
2) Convert circle to a polyline
3) Apply the remove arcs edit to the polyline
4) In the transform window, apply the scale transform to either the X or Y axis. The scale amount is the ratio of the minor to major axes.