Thanks to Aaron Stebner's post, I was able to easily get Visual Studio .NET 2005 to provide IntelliSense (based on XSD) for custom XML files. The best approach seems to be dropping a new schema catalog file along with the referenced XSD file(s) into the %VsInstallDir%/xml/schemas/ directory. It appears that VS monitors this directory for changes. This approach is nice because it doesn't involve updating any of the default VS installation.