For a while I wanted to have the template files of DasBlog HTML highlighted but I was unable to find the answer. Today one of my colleagues showed me the answer which involves a bit of tinkering in the registry settings for Visual Studio.

1. Open HKEY_LOCAL_MACHINE\Software\Microsoft\VisualStudio\<version of VS, i.e. 7.1 for 2003>\Languages\File Extensions
2. Copy the GUID found in the extension.
3. Create a new key with the name of the extension you want highlighted.
4. Paste the GUID you found in step into the value named (Default) and the your custom extension into the value named unused.

Thanks to the newest additional to the Vertica crew for that little tidbit.