Event IDs
Every event contains information on what action occurred as well as related information. The Event ID is the unique identifier for particular types of events that occur on Windows machines.

Because there is an unmanageable number of different event IDs, there are few reliable single sources for information to help decrypt them. The resources below are the best available.

Other resources:

Search Windows 2000 Event and Error Messages
Provided by Microsoft. Search for particular events or errors and download a .csv file containing Windows errors and events.

Glossary of Windows 2000 Services
Provided by Microsoft. Search through and download the definitions of the roughly 100 services that may be referenced in your events.

Events and Errors Message Center
Provided by Microsoft. Search by OS and by source or ID for particular messages.

Windows 2003 Support Center
Provided by Microsoft. Search the phrase "Event ID XXXX," using a particular event ID you wish to research.

Windows 2000 Support Center
Provided by Microsoft. Search the phrase "Event ID XXXX," using a particular event ID you wish to research.

Windows NT 4.0 Support Center
Provided by Microsoft. Search the phrase "Event ID XXXX," using a particular event ID you wish to research.

eventlogs.blogspot.com
See things through the eyes of the development department in a leading SEM / SIEM software firm and keep up on the complexities of the Windows Event Log and eventing.