  We probe the stau-neutralino co-annihilation domain of the parameter space
allowed by the current experimental bounds on the light Higgs mass, the b-> s
\gamma decay, and the amount of neutralino cold dark matter within the
framework of minimal SUGRA models at a 500 GeV e+e- linear collider. The most
favorable signals of SUSY are stau pair production and neutralino pair
production where the small mass difference between the lighter stau and the
lightest neutralino in the co-annihilation region is ~5-15 GeV and hence
generates low-energy tau leptons in the final state. This small mass difference
would be a striking signal of many SUGRA models. We find that a calorimeter
covering down to 1^o from the beams is crucial to reduce the two-photon
background and the mass difference could be measured at a level of 10% with 500
fb^-1 of data where an invariant mass of two-tau jets and missing energy is
used as a discriminator.
