For future generations who search on this question, here's what I eventually did:
1) Used 3dmaskavg to extract voxel values and (i,j,k) coordinates
2) Used the ORIGIN and DELTA attributes in the +orig.HEAD file to convert the (i,j,k) coordinates to (x,y,z) coordinates in the original space
3) Used Vecwarp to convert the (x,y,z) coordinates to Talairach space
Cheers.
-- Erich