I will be traveling to Italy this spring. A friend of mine was there a few years ago and they were able to get an art student studying in Rome as a guide for the Vatican. I can't seem to find any info on the internet regarding this type of service. Also, we will be in Florence and Venice. Maybe you know of guides there?
Your friend may have been referring to Angel Tours. Their guides are art/history students or graduates. www.angeltoursrome.com Have not been on one of their tours, but most of the reviews I have seen have been favorable.
The Vatican's official website offers a great tour for 23.5 euro a person that includes the admission ticket. You reserve online and get to bypass the line which was pretty bad when we were there last spring.
I'd say you are referring to Angel tours. I did the Vatican tour with them last year and really enjoyed it. I met other people on this tour who had done other tours with them and were very pleased. Look up www.angeltoursrome.com