  We construct the open string boundary states corresponding to various
time-dependent deformations of the D-brane and explore several ways in which
they may be used to study stringy soliton collective coordinate quantum
dynamics. Among other things, we find that D-strings have exact moduli
corresponding to arbitrary chiral excitations of the basic soliton. These are
presumably the duals of the BPS-saturated excitations of the fundamental Type
IIB string. These first steps in a systematic study of the dynamics and
interactions of Dirichlet-brane solitons give further evidence of the
consistency of Polchinski's new approach to string soliton physics.
