I've heard it can be hard to find, and I can't find a map of the inside of Termini station. Thanks! :) One week until I leave, I can't wait! And I couldn't have done it without y'all's help! :)
It is large facility that is hard to miss. It is on the far right side (as your face the tracks) at the ground level. You can also reach it from the outside by walking down the sidewalk along that side of the station. Just look for the sign.
As Frank says, it to the "south" or right of Track #24 (if you're coming from the main terminal area) in the "Ala Termini" area of the train station. It is just adjacent to the car rental booths so if you follow the signage to the car rental area, you'll find the Desk. The road that Frank mentions is Via Giovanni Giolitti. This link has a picture of the signage towards the bottom of the post **** http://tinyurl.com/roma-termini ****
Hopefully they are more helpful and useful than those located in the city. I have not had much luck with those.