Microsoft Knowledge Base Article 899191 contains the following summary and introduction:

SUMMARY

Microsoft Windows Server 2003 Service Pack 1 (SP1) and Microsoft Windows XP Service Pack 2 (SP2) include many security-related updates and changes. Some of these changes affect the Microsoft Distributed Transaction Coordinator (MSDTC) service.

These changes can be accessed by using the updated Security Configuration dialog box that is available in the Component Services administrative tool.

After you install Windows Server 2003 SP1 or Windows XP SP2, some changes are made to the default security settings that cause Distributed Transaction Coordinator traffic to fail over the network. In this situation, you may receive one or more error messages or error codes.

By modifying the settings in the Security Configuration dialog box, you can help control how the Distributed Transaction Coordinator service communicates with remote computers over the network.

INTRODUCTION

This article describes new functionality in the Microsoft Distributed Transaction Coordinator (MSDTC) service in the following operating systems:

Microsoft Windows Server 2003 Service Pack 1 (SP1)
Microsoft Windows XP Service Pack 2 (SP2)

The Distributed Transaction Coordinator service coordinates transactions that update two or more transaction-protected resources. Transaction-protected resources include databases, message queues, and file systems. These transaction-protected resources may be located on a single computer or may be distributed between many networked computers.