Not sure if this is PS07 or PS03...
Long story short, yes. Dale is correct that only one person can edit
the project at one time, but you can have multiple PMs with access to
edit the project.
If PS07, you can have only a single "Project Owner", but you can have
multiple "Status Manager"s. The SM is basically the owner for a given
task (assigned at the task level). You can setup the security in PS
to allow PMs to edit projects on which they are team members and then
they can open the project in Pro07 and make themselves the status
manager of certain tasks, which will probably work for you. So you
can setup security to allow other PMs to edit the project, and you can
also use the status manager feature, which gives you control over
updates - i.e. who will receive the task updates from Team Members for
each task.
If PS03, similar security can be setup using the Categories and
groups. There is no status manager, but what you can do is have
another PM open the project, highlight the tasks they will own, then
go to Collaborate-->Publish-->Republish Assignments. In the
"Republish Assignments for:" drop-down, choose Selected Items, then
check the box at the bottom for "Become the manager of these
assignments".
So the security settings I think you would need is to have have a
category that applies to Projects that the User is a TM on, add the PM
group to this category and set the category permissions to allow them
to save and publish the project (or however you need it to be...).
Then any user that is in the PM group and is on the project team
(added through Tools-->Build Team From Enterprise) can edit the
project.
I hope this is clear...