  We study the low energy effective theory describing the dynamics of
D-particles. This corresponds to the quantum mechanical system obtained by
dimensional reduction of $9+1$ dimensional supersymmetric Yang-Mills theory to
$0+1$ dimensions and can be interpreted as the non relativistic limit of the
Born-Infeld action. We study the system of two like-charged D-particles and
find evidence for the existence of non-BPS states whose mass grows like
$\lambda^{1/3}$ over the BPS mass. We give a string interpretation of this
phenomenon in terms of a linear potential generated by strings stretching from
the two D-particles. Some comments on the possible relations to black hole
entropy and eleven dimensional supergravity are also given.
