First of all, I really want to spell centre the UK way but I can't!!!!

 Anyway, the TechNet website and newsletter have included System Centre a lot lately and how it must be confusing because of all the sepearte products under the "System Centre" unbrella, so here is a good overview I found on the System Centre pages on ms.com

System Center Overview

Microsoft System Center plays a central role in the Microsoft vision to help IT organizations benefit from self-managing, dynamic systems. System Center solutions capture and aggregate knowledge about your infrastructure, policies, processes, and best practices so your IT staff can build manageable systems and automate operations in order to reduce costs, improve application availability, and enhance service delivery.

System Center solutions are tuned to simplify management of the systems and applications your company already has implemented, including Microsoft SQL Server, Microsoft Exchange Server, the Microsoft Office system, and the Microsoft .NET Framework. In addition, System Center solutions interoperate with third-party management tools so you can make the most of your existing investments and build on the System Center foundation with confidence. Already used by the majority of Fortune 500 companies, System Center solutions provide the reliability, scalability, and security required to manage the most mission-critical IT systems, applications, and services.

With an aim to enable self-managing dynamic systems, System Center solutions close the gap between development, operations, and IT by evaluating dependencies and optimizing business process performance from deep inside the operating system, applications, and composite services and workflows. These solutions also provide comprehensive management of physical and virtual environments, resulting in improved efficiencies and better control.

System Center Operations Manager
Microsoft System Center Operations Manager 2007 (formerly known as Microsoft Operations Manager), affords you a comprehensive, overall view of the health of your IT environment. Track thousands of event and performance monitors across hundreds of operating systems and applications. In addition, get best-of-breed, end-to-end service management for the Windows platform and access to more than 50 management packs for various Microsoft software applications. Finally, automate routine, redundant tasks to increase efficiency and enable greater control of your IT environment.

System Center Configuration Manager
Microsoft System Center Configuration Manager 2007 (formerly known as Microsoft System Management Server) drives IT productivity and efficiency by reducing manual tasks and enabling you to focus on high-value projects, maximize hardware and software investments, and empower end-user productivity with the right software at the right time. Configuration Manager contributes to a more effective IT department by enabling secure and scalable operating system and application deployment and desired configuration management, enhancing system security, and providing comprehensive asset management of servers, desktops, and mobile devices.

System Center Data Protection Manager
Microsoft System Center Data Protection Manager 2006 optimizes and speeds disk-based backup and recovery, delivers consistent data protection, and increases your IT organization’s operational efficiencies. For example, recover information quickly by copying content from a production server and speed data recovery with always-accessible disks. Data Protection Manager also supports near-continuous data protection with centralized backup of branch offices and backup enhancements within the data center. Finally, help lower the total cost of your data-protection environment by consolidating backup efforts at the data center, empowering end users to perform their own recoveries, and implementing out-of-the-box reporting and monitoring functionality.

System Center Essentials
Microsoft System Center Essentials 2007 is a proactive, unified management solution that enables IT professionals in your midsize organization to more efficiently secure, update, monitor, and troubleshoot your IT environments. Essentials 2007 provides a unified solution to help optimize a broad set of tasks across your entire IT environment and a single console from which you can view and manage all of your servers, clients, hardware, software, and IT services. In addition, Essentials 2007 helps you proactively monitor your IT environment, simplifies complex management tasks, and automates system updates and data collection for your IT environment. The end result is a more efficient, secure, and up-to-date IT environment.

System Center Virtual Machine Manager
Microsoft System Center Virtual Machine Manager 2007 is a stand-alone management application for a virtual data center. Virtual Machine Manager increases use of your physical server, allows you to centrally and virtually manage your infrastructure, and lets both administrators and end users rapidly provision new virtual machines.

System Center Capacity Planner
Microsoft System Center Capacity Planner 2006 is a predeployment, capacity-planning solution that provides best-practice guidance, hardware-specific knowledge, and "what if" scenario planning. For example, with Capacity Planner you can make solid architecture decisions as you plan to deploy Exchange Server 2003 or Operations Manager, plan ahead for IT purchases, and receive automated reports to proactively manage current and future performance issues.