  We apply ideas that have appeared in the study of D-branes on Calabi-Yau
compactifications to the derivation of the BPS spectrum of field theories. In
particular, we identify an orbifold point whose fractional branes can be
thought of as ``partons'' of the BPS spectrum of N=2 pure SU(N) SYM. We derive
the BPS spectrum and lines of marginal stability branes near that orbifold, and
compare our results with the spectrum of the field theories.
