  We report the discovery of twin kHz QPOs in the X ray flux of XTE J1807--294,
the fourth accreting millisecond pulsar (AMP). This is the second AMP
exhibiting twin kHz QPOs. In contrast to the first case, SAX J1808.4--3658, the
frequency separation $\Delta\nu$ between the kHz QPOs is consistent with the
pulse frequency (190.6 Hz), not with half that value, confirming for the first
time from pulsation measurements the inference, based on burst oscillations,
that 'slow rotators' (spin frequency less than 400 Hz) have $\Delta\nu$
approximately equal to the spin frequency. While the QPOs move in frequency
together over a range of more than 200 Hz, $\Delta\nu$ remains constant with an
average value of 205$\pm$6 Hz. Variability components were found in the 5--130
Hz range similar to those seen in other LMXBs. The correlations between the QPO
and noise frequencies are also similar to those in other sources, but shifted
by a factor of 1.59 in kHz QPO frequencies, similar to the factor 1.45 shift
found for SAX J1808.4--3658. Our results argue in favour of a spin-related
formation mechanism for twin kHz QPOs and against a spin-related cause of the
shift in the frequency correlations.
