  The equivariant and ordinary cohomology rings of Hilbert schemes of points on
the minimal resolution C^2//G for cyclic G are studied using vertex operator
technique, and connections between these rings and the class algebras of wreath
products are explicitly established. We further show that certain generating
functions of equivariant intersection numbers on the Hilbert schemes and
related moduli spaces of sheaves on C^2//G are tau functions of 2-Toda
hierarchies.
