VIBRATZ should be able to read input files written for the old DOS version, called VIBRAT. The Open command recognizes only files with extension .VIB and .VBR, so it will be necessary to add the .VIB extension (not .VBR).
The only change which is likely to affect the calculation of frequencies is the treatment of "2-coordinate" 3-atom angles (Angle forces). In the old VIBRAT, if the "2-coordinate" option was selected, a second bending coordinate was constructed with s-vectors perpendicular to those of the standard or in-plane coordinate, and this coordinate was assigned a force constant f' related to the standard force constant by f' = f (1+cos(theta) /2). Currently, for such "2-coordinate" angles, the second force constant f' is exactly equal to the first one. For 180 degree angles there should be no difference. If you want to keep the internal coordinates as defined by the old version, you can define two separate angles, one in-plane and one out-of-plane, with the force constant for the second as above.
The atomic displacements for the second coordinate in 2-coordinate angles were not computed correctly in the old version, and least-squares refinement of these forces was not effective. This has been corrected.
Computation of the polarizability tensor has changed (see Theory and Implementation), but this has little effect on spatially averaged Raman intensities, keeping in mind that the intensity estimates are qualitative or semi-quantitative at best.