The location of the registry will differ depending on whether you have a 32-bit or 64-bit operating system.
For a 32-bit installation of Windows, use:
HKLM \ SOFTWARE \ Microsoft \ VisualStudio \ 9.0 \ Languages \ File Extensions
And for a 64-bit installation of Windows use:
(64-bit) HKLM \ SOFTWARE \ Wow6432Node \ Microsoft \ VisualStudio \ 9.0 \ Languages \ File Extensions
As @David points out, you must create a new key for your extension (for example, .tab, .prc, etc.) and set the default value to "{FA6E5E79-C8EE-4D37-B79A-5067F8BD5630}".
source share