For Working and Published, MSPS 2007 has two separate databases "Draft" and
"Published" respectively.
When you first save a project to project server, it stores it in the Draft
database as a "Working" copy only. If you select Published mode you will
not be able to see it. Only after you publish it for the first time will it
push the data to the Published database at which point it is available to
view through Project Web Access or PWA. You wll also now see it when
selecting Published mode in Project Professional.
From then on, when you access the schedule from Working (Draft DB) you can
choose to only save it which will update the Draft DB but not the Published
DB. Or you can publish it which will synch up the Draft DB data with the
Published DB data.
The idea and intent is that you can have a "Working" copy that you don't
publish until you are ready to have the rest of the organization see it as a
final version via PWA.
Jonathan