  D-instantons are used to probe the near-horizon geometry of D3-branes systems
on orbifold spaces. For fractional D3-branes, D-instanton calculus correctly
reproduces the gauge beta-function and U(1)_R anomaly of the corresponding N=2
non-conformal Super Yang-Mills theories. For D3-branes wrapping the orbifold
singularity, D-instantons can be identified with gauge instantons on ALE space,
providing evidence of AdS/CFT duality for gauge theories on curved spaces.
