I have read and responded to several questions about the Data Migration Manager (DMM). DMM is a robust and flexible tool that provides the ability to migrate data into the CRM system. Microsoft has done a great job in providing this tool, and when installed correctly provides an excellent way to provide value by getting necessary data into the application.
Before attempting to install and use the tool, it is a good idea to gain a solid understanding of the application. This will minimize the potential for unexpected issues and may save you a lot of troubleshooting hours. Below are links that you can access to learn more about the tool, how to install and use it correctly. I encourage you to read through this information and also read through the help files in DMM.
Microsoft Dynamics CRM 4.0 Data Migration Manager Download
How to Use DMM
Data Migration Manager Tips and Tricks
Microsoft Dynamics CRM 4.0 Data Migration Manager Readme
Data Migration and Import: Using field delimiter characters in the source files
Data Migration and Import
Data Migration Wizard: Express versus Standard Mode
Advanced Data Migration Map Editor for CRM 4.0
Donna Edwards 