  We investigate tachyon dynamics with an inverse power-law potential $V(\phi)
\propto \phi^{-\alpha}$. We find global attractors of the dynamics leading to a
dust behaviour for $\alpha > 2$ and to an accelerating universe for $0 < \alpha
\le 2$. We study linear cosmological perturbations and we show that metric
fluctuations are constant on large scales in both cases. In presence of an
additional perfect fluid, the tachyon with this potential behaves as dust or
dark energy.
