Professional, Web Access, and Server editions
In its basic format, the Professional edition of Project 2007 is identical to the Standard edition. What is gained in functionality however complements a more enterprise-level IT environment. The professional edition can be utilized as a standalone product, but to do so really hinders the software's ability to shine. After all, the cost difference between the two editions is significant, so not using the extra functions would be a true waste of money.
However, in order to use the advanced functions of the Professional edition, you will need to have Project Server 2007 installed on a server as well. This setup gives you access to powerful collaboration tools, for example, being able to assign tasks to individuals on a project and have it appear on their task lists in Outlook. The software also allows for management of shared resources, something that is often difficult when you're one project manager in a large corporate environment. The professional edition of Project 2007 also helps to create reports across multiple projects, which can be run by different project managers.
A significant advantage to the professional edition of MS Project 2007 is that project management team members can be selected using Active Directory. The benefits of an Active Directory domain - groups, distribution lists, etc - can help ease the management of resources and assignments for organizations. The ability to assign different levels of security access to project data based upon group membership is also an added advantage.
In an organization where there are multiple projects, across multiple departments, with multiple project managers, Project Server is a useful necessity. The server edition is a great way to have a central repository of project data in the event that your environment is highly complex or where collaboration among the various project teams is essential. The advantage of having a central server for all of your project data means that everything can be backed up in one location. More project data can be utilized for reporting purposes, or resources can be allocated from across multiple projects or divisions due to its centralized location.
There are some downsides to implementing Project Server 2007, though. For one thing, having all of your projects on a server creates a single point of failure (assuming you're not running a "farm" or multiple installations of Project Server). If the server crashes, all access to the project data is compromised. There is a cost therefore in providing ample backup and recovery assets, as well as the cost of the hardware to adequately run the server. Project Server 2007 requires the use of a SQL server, which in real terms means a second server just for the SQL database (in most environments).
Project Server requires a great deal of computing resources to be highly responsive, so for most implementations you cannot put the Project server on the same hardware as the SQL server. The cost for licensing the server also depends upon your implementation, which can only be answered when you contact Microsoft (or a reseller) for pricing. And finally, your environment will need server administrators to manage the servers. If you're in an environment where Project Server 2007 seems like a good resource however, you most likely already have a dependable IT division to handle this.
Project 2007 Web edition is an alternative interface that can be used along with Project 2007 Server edition. It is basically a thin-client for accessing the project data, whereas the Professional edition is a "thick-client". The per user licensing cost for the Web edition is less than providing everyone a full copy of Professional or Standard, since the cost is based upon how many Client Access Licenses (CALs) are purchased for Project 2007 Server. And access to project resources can still be managed via security on the Project server, in the same way it is handled for Project 2007 Professional edition users. When users log in, they have access to see any projects they have been assigned user rights.
The software provides Gantt chart views just like the standalone versions, but it's in a web interface that loads and updates as data on the server is updated. Of course the functionality is diminished, but the full versions of Professional or Standard can be provided for those individuals who need those advance functions. Web edition is ideally for individuals who only need to be able to access the project data that affects them, such as teams assigned certain project tasks. Depending on permissions assigned, user can update their projects where necessary without the need for the full software, and they don't necessarily need to know how to use the full functionality that comes with Standard or Professional. This can save the organization money for both licensing as well as training costs.