You can skip straight to the section abot 1/3rd of the way down titled Setting Up Your XML Configuration File: XML Configuration files in SQL Server Integration Services[/url]

For your situation, unlike in the article where Robert selects the alue property of several variables, you will want to find the section for Connection Managers and select the ConnectionString property of your chosen Connection Manager. When you complete the Package Configuration wizard go look at the resulting .dtsConfig file in notepad and it will be easy to tell what you need to change when you deploy the Package and config file to a new server.

One wrinkle in using XML Package Configurations to be aware of, the path to the .dtsConfig file is stored in the .dtsx file when you set it up the way Robert has meaning that the path you choose to store the file must exist on all servers where you plan to deploy it. Sometimes this is difficult to predict. An alternative is to use an Indirect Configuration where the path to the .dtsConfig file is stored in an Environment Variable, but that has it's own pluses and minuses. Post back with specific questions if you have doubts or want to discuss further.