Your responsibility as a publication chair is to ensure that the proceedings of ACL and all of its associated events are prepared correctly, uploaded to the local website for your ACL, and archived at the Anthology. You interact with other people in the following ways.
The general chair is the person who first asked you to be a publication chair. They are responsible for the overall success of the conference, so if you are ever uncertain about a decision, it is good style to run it by the general chair first – especially if you are deviating from they way it was done before, or anticipate that others might not agree with you.
You will frequently coordinate with the program chairs. You will need to coordinate the time you get for preparing the proceedings with their decisions regarding the camera-ready deadline and the time when they make the schedule for the conference. They will also set up the START system in which you do most of your work, make decisions about page limits for papers, and so on.
The job of the local chairs includes the website for the conference, to which you will eventually contribute the proceedings package that is still called “CD-ROM” for historical reasons. The local chairs are also responsible for preparing the conference handbook. The handbook includes the schedule of talks and abstracts for all the papers, and you will therefore coordinate with the local handbook person to contribute these. The local chairs may also have artwork for that year’s conference produced, which you may want to share as the cover page for the proceedings.
The student chairs, demo chairs, tutorial chairs, and the chairs of the individual workshops and co-located conferences each produce a separate volume of the proceedings (“books”). These people are collective known as the book chairs, and your sanity in the weeks before the conference will depend very heavily on how well you manage their work. Each book chair is responsible for preparing their own book, but you are responsible for making sure that their books are produced correctly. So there will be intense interaction.
There are also workshop chairs for the whole conference, who organize the work of the chairs of the individual workshops. Their work centers around the selection of the workshops, and is therefore finished long before yours really starts. Your primary interaction with them is to set the camera-ready deadline for the workshops.
The director of the ACL Anthology is in charge of maintaining the ACL Anthology. They will assign you Anthology identifiers for all the books in your conference, which you will then pass on to the individual book chairs. They will also eventually ask you for the complete proceedings of all the books together so they can upload them to the Anthology. Information on this process can be found here.
Priscilla Rasmussen is the person to go to when nobody else can help. One item that is specifically her job is to obtain ISBN numbers for all the books once you ask her.
The people at Softconf (the company that runs the START system) will be your best friends throughout the publication process. START, and the version of the ACLPUB system inside of it, are battle-tested pieces of software, but things still go wrong. In these cases, Rich Gerber and his colleagues are amazingly willing to help.