As far as your Vista installation is concerned the files are where they've always been - in specific folders on the D: drive. You didn't unistall it so provided all the files are found where expected it will happily run.
Provided the Win7 installation puts the files in the same place it's effectively no different to wiping the D: drive and restoring it from a back-up.
Updating the software (a security patch for instance) might cause problems as the file versions may no longer match what's recorded in the registry for the other OS. It may not cause problems or applying the patch in both OSes might fix it.