normal coordinate displacements

 Dear CCLers,
 I'm searching for a program that can do the following:
 Transform cartesian normal coordinate displacements into
 internal symmetry coordinates, and generate with them
 (stepwise and iteratively) a new displaced geometry for each vibration.
 This should be not as disturbed as if one would directly
 add cartesian normal coordinates to the minimum geometry
 which only holds for infinitisimal displacements.
 I know that a program named BALGA (in conjunction with some
 help programs) can do this. But our version seems only to handle small
 systems, and I need a program that works with more than 20 atoms.
 Has anybody written or knows of such a program?
 Preferably, it should directly read in cartesian normal coordinates
 from quantum chemistry packages like GAUSSIAN, GAMESS, ...
 Any hints are welcome! Thank you very much in advance
 Dipl.-Chem. Wibke Sudholt
 Institute of Theoretical Chemistry
 Duesseldorf, Germany
 wibke' at \`