Here is the list of components in Microsoft's EPM Solution:
Portfolio Server
Project Server
    PWA (Project Web Access)
    SharePoint
    Microsoft Project

Here is a matrix of these components aligned to roles within an organization.
Ranking in value to Role with 1 being highest.  Blank indicates little to no value.

Here is a brief summary of each component:
This provides the justification for the value ranking.

Portfolio Server - A top down planning tool.  Used to help align potential projects to organization strategy.  Useful in determining which projects are of priority and should be initiated given the constraints and objectives of the organization.

Project Server - Best to describe as a suite of the following three products:

PWA (Project Web Access) - Summarizes all project schedules and resource information across the organization.  Information is made available via the web.  Project progress is entered via the web.  Eliminates the need for Team Members to install MS Project.   Built in security allows for customized access to information.

SharePoint - This is the collaboration component of the suite.  The Project Manager becomes the "Website Administrator" of the SharePoint site for his/her project.  Features include Document Management, Issue and Risk Management, Wiki, Work Flow, Discussion Board and many more "canned" views (web parts).  Additional levels of security can be established.

Microsoft Project (Professional) - Connecting to the Enterprise Resource Pool, this is the tool used for detailed planning and resource assignment.  Tightly integrated with PWA for reporting and tracking project progress.  Also integrated with SharePoint for Deliverable reporting.

For more information on these components, try these links:
Portfolio Server
Project Server
    PWA
    SharePoint
    Microsoft Project