afni.nimh.nih.gov

What do you mean by "client side"? The 3dmaskdump command line function can do something like what you want, but not via interactive clicking. (See the recent thread on "Readout of activated voxels" for more info on this program.) The 3dclust program will find contiguous clusters of activated voxels and print out information about each cluster, but not about each voxel within the cluster.

bob cox