  This paper gives a twistor-string formulation for all tree amplitudes of
Einstein (super-)gravities for N=0 and 4. Formulae are given with and without
cosmological constant and with various possibilities for the gauging. The
formulae are justified by use of Maldacena's observation that conformal gravity
tree amplitudes with Einstein wave functions and non-zero cosmological constant
will correctly give the Einstein tree amplitudes. This justifies the
construction of Einstein gravity amplitudes at N=0 from twistor-string theory
and is extended to N=4 by requiring the standard relation between the
MHV-degree and the degree of the rational curve for Yang-Mills; this
systematically excludes the spurious conformal supergravity gravity
contributions. For comparison, BCFW recursion is used to obtain
twistor-string-like formulae at degree zero and one (anti-MHV and MHV) for
amplitudes with N=8 supersymmetry with and without cosmological constant.
