  We determine the low energy dynamics of monopoles in pure N=2 Yang-Mills
theories for points in the vacuum moduli space where the two Higgs fields are
not aligned. The dynamics is governed by a supersymmetric quantum mechanics
with potential terms and four real supercharges. The corresponding superalgebra
contains a central charge but nevertheless supersymmetric states preserve all
four supercharges. The central charge depends on the sign of the electric
charges and consequently so does the BPS spectrum. We focus on the SU(3) case
where certain BPS states are realised as zero-modes of a Dirac operator on
Taub-NUT space twisted by the tri-holomorphic Killing vector field. We show
that the BPS spectrum includes hypermultiplets that are consistent with the
strong- and weak-coupling behaviour of the Seiberg-Witten theory.
