Hi Jim
Unfortunately this is exactly what IDR was designed to prevent you from doing- restoring a backup where something is meant to be different.
You have two options, but my recommendation would be to invest in something such as one of hte Acronis disk resizing softwares, or go about this the long way by throwing IDR in the bin, building a new OS install, installing Veritas and then restoring your backup.
Be aware that this will be a "forced catastrophe" in that if there are any issues you may have with your backups, you will find out the hard way.