Those locations are for Apple's templates. While it is technically possible to place your templates with Apple's (I placed some of my SDL and OpenGL project templates with Apple's project templates and had no problems), the Xcode 3 release notes say you're supposed to place your templates in a different location. Project templates belong in the following location:
Library/Application Support/Developer/Shared/Xcode/Project Templates
File templates belong in the following location:
Library/Application Support/Developer/Shared/Xcode/File Templates
You're going to have manually create all the folders after Application Support in the path.
If you use the paths I just mentioned, your project and file templates will be available for all users on your Mac and be available for use in both Xcode 3 and Xcode 2.5. If you want to restrict your templates to a specific version of Xcode, replace Shared with the Xcode version number. If you want only a single user to be able to use your templates, start the path with Username/Library.