This example sets the horizontal and vertical offsets for the shadow of shape three on the first slide in the active presentation. The shadow is offset 5 points to the right of the shape and 3 points above it. If the shape doesn't already have a shadow, this example adds one to it.
Set myDocument = ActivePresentation.Slides(1)
With myDocument.Shapes(3).Shadow
.Visible = True
.OffsetX = 5
.OffsetY = -3
End With