We develop a shell-model Monte Carlo method to calculate densities of state
s with varying exciton (particle hole) number. We then apply this method to
the doubly closed-shell nucleus Ca-40 in a full Os-1d-0f-1p shell-model sp
ace and compare our results to those found using approximate analytic expre
ssions for the partial densities. We find that the effective one-body level
density is reduced by approximately 22% when a residual two-body interacti
on is included in the shell-model calculation. [S0556-2813(99)04010-8].