In the Attach to Motion Path
Options that appear, do the following:
Turn Follow on.
When Follow is
on, the Front Axis and Up
Axis options determine which of the three local rotation
axes sets the front and up of the object respectively. See
Follow.
Select the axis you chose to represent
the front of your object as the Front Axis,
and select the axis you chose to represent the up direction of your object
as your Up axis.
Click Select by object type in
the Maya status line (tool bar) to switch to object selection mode.
Select the object, then -click
the curve in your scene that you want as your motion path.