  Measurement of the tau lepton polarization in \eett\ is an important
electro-weak measurement at ILC and other future electron-positron colliders.
In this paper we discuss several methods to extract polarimeter information for
\eett\ events at the nominal centre-of-mass energy, and develop a new method,
based on charged particle impact parameter measurement, which can accurately
reconstruct tau momenta even in events with significant Initial State
Radiation.
  In future work we will extend the study to estimate the precision with which
the tau polarization can be measured at ILC-250, both for high-mass tau pairs
and for those which radiatively return to the $Z^0$ peak. This will complement
our past study which showed that the tau polarization can be measured to better
than 1\% at the ILC-500.
