Windows Time

 Maintains date and time synchronization on all clients and servers in the network. If this service is stopped, date and time synchronization will be unavailable. If this service is disabled, any services that explicitly depend on it will fail to start.

Windows Search

 Provides content indexing and property caching for file, email and other content (via extensibility APIs).  The service responds to file and email notifications to index modified content.  If the service is stopped or disabled, the Explorer will not be able to display virtual folder views of items, and search in the Explorer will fall back to item-by-item slow search.

Windows Management Instrumentation

 Provides a common interface and object model to access management information about operating system, devices, applications and services. If this service is stopped, most Windows-based software will not function properly. If this service is disabled, any services that explicitly depend on it will fail to start. This service is used a lot in the enterprise environment in scripting events on computers. In the home area, there is no use for it and can be disabled. If in the future you ever have any problems with installing programs, try re-enabling this service again since some, not all, tend to use it.

Windows Image Acquisition (WIA)

Provides image acquisition services for scanners and cameras.

Windows Firewall

Windows Firewall helps protect your computer by preventing unauthorized users from gaining access to your computer through the Internet or a network.

Windows Error Reporting Service

 Allows errors to be reported when programs stop working or responding and allows existing solutions to be delivered. Also allows logs to be generated for diagnostic and repair services. If this service is stopped, error reporting might not work correctly and results of diagnostic services and repairs might not be displayed. This service has always been a favorite for power users to disable. I’m not going to lie, it will give you a slight performance gain if you disable it since less overhead = more resources for your apps. However, Windows Vista is in Beta! Why wouldn’t you want Microsoft to hear about the problems you are having. Don’t you want them to be aware of issues you are having?

Windows Defender

 Scan your computer for unwanted software, schedule scans, and get the latest unwanted software definitions.

Windows Audio Endpoint Builder

Manages audio devices for the Windows Audio service.  If this service is stopped, audio devices and effects will not function properly.  If this service is disabled, any services that explicitly depend on it will fail to start.

Windows Audio

 Manages audio for Windows-based programs.  If this service is stopped, audio devices and effects will not function properly.  If this service is disabled, any services that explicitly depend on it will fail to start

WebClient

Enables Windows-based programs to create, access, and modify Internet-based files. If this service is stopped, these functions will not be available. If this service is disabled, any services that explicitly depend on it will fail to start.