Finally, something I know a little about.
The big enemy in vet clinics is pet hair. Mount the computer as high as possible to keep hair and dust to a minimum. If your father does not want to change software then the "physical to virtual" idea sounds like an idea you may want to look into.
I will let others comment on actually hardware but one thing you should talk to your dad about is good backups. Very few vet clinics back up frequently enough and even fewer know how (or when) to restore a back up. Set up a clear back up plan and teach the staff how to restore a back up; they should also be instructed on reasons to restore a back and be sure they understand what will be lost (everything since their last back up). I would recommend backing up to thumb drives and have a different drive for each day of the week. Also back up to CD or DVD once a week/month and archive.
I know of one vet clinic w/ a laptop plugged into a UPS w/ a low power printer kept on a cart but not connected to any other computers. When they had a snowstorm collapse the roof in the room w/ their sever one winter they rolled out the cart restored the back up and kept on seeing patients. Some veterinary software is written w/ a version for vets to use in the truck on farm call that then integrates everything back to the main computer when they get back to he office. If your dad is updating software as well, AAHA Trends magazine will have a write up on all the software this summer (june?)