Conformal supergravity arises in presently known formulations of
twistor-string theory either via closed strings or via gauge-singlet open
strings. We explore this sector of twistor-string theory, relating the relevant
string modes to the particles and fields of conformal supergravity. We also use
the twistor-string theory to compute some tree level scattering amplitudes with
supergravitons, and compare to expectations from conformal supergravity. Since
the supergravitons interact with the same coupling constant as the Yang-Mills
fields, conformal supergravity states will contribute to loop amplitudes of
Yang-Mills gluons in these theories. Those loop amplitudes will therefore not
coincide with the loop amplitudes of pure super Yang-Mills theory.Comment: 43 pages harvmac tex, added footnote to introductio