To be sure to get intellisense in XML files, you can try the two methods detailed by Jopx here. I say try, cause it didn't work for me. What DID work, was adding a folder with links to the xsd files to the project, as shown by Tony Bierman here.
To do this,
- Add a folder to the project
- Click Add Existing Items
- Navigate to C:/Program Files/Common Files/Microsoft Shared/web server extensions/12/TEMPLATE/XML
- Select all the schem files (not sure what they all do, but it doesn't hurt)
- Click the little dropdown to the right of the Add button and select Add as Link.
- Done. Intellisense.
Sorry- doesn't help with your ddf files...