Are they different terms for the same thing or do they have different roles and responsabilities?
It's not quite your question, but at Microsoft, the Program Manager has tech responsibility, and the Product Manager has marketing responsibility. Is this at all relevant to what you asked?
They're related, but have a different focus:
A project leader will typically be responsible for more of the day-to-day running of the development effort. They should have a more technical focus than a project manager, and they're more likely to be involved in helping determine software architecture, release details, etc. A development team's senior developer or senior architect will often fill the role of the project leader in this respect.
A project manager will typically be more focused on the business side of the development effort, so they're going to be talking about meeting business requirements, managing development budgets, etc. Less of the day-to-day technical stuff and more of the fluffy business stuff.
For me it usually means:
- Project-Leader: Manages the internal side of the project. He/she makes sure the development team is meeting the needs and requirements of the project.
- Project-Manager: Manages the external, or customer, side of the project. He/she makes sure the project is meeting the needs and requirements of the customer.
I agree with Andrew. In a nutshell, the leader can and actually does the technical work. The manager may or may not be able to do the technical work and their role as manager is focused on coordinating the pieces - engineering, marketing, production, et al.
A project leader will tell the team "All of you, take these axes and start cutting down these trees asap."
A project manager will climb up a tree, look around and say "Shit, we are in the wrong forest."
Project Leader is usually a member of the team who has been chosen to monitor/manage the lower level/technical details of the Project. Project Manager manages the whole project and usually does not go as technical as the project leader. The Project Leader reports to the project manager.
you should all see the difference between the project manager, and project leader from PMI point of view. see the PMBOK4 for the answer.