How to: Add a Content Type to a Site
You can specify content types to include in a site definition, so that each time a user provisions a site of that type, Windows SharePoint Services makes those site content types available on the site by default.
Site definitions can be included in Features. For more information, see Working with Features.
After a user provisions a site, you can add content types to that site through the Windows SharePoint Services object model.
Specifying Content Types in a Site Definition
To specify a content type to include in a site definition, you first create the content type as a separate Feature, and then reference that Feature in the site definition.
To specify a content type to included in a site definition
Create the content type as a separate Feature.
For more information, see Working with Features.
Reference that Feature in the feature that defines your site:
In your site Feature, open the XML file that defines your site.
In the Project element, under the Categories and Category elements, add a reference to the content type Feature in either the SiteFeatures or WebFeatures element. For example:
<Feature ID="00BFEA71-1C5E-4A24-B310-BA51C3EB7A57" />
<Feature ID="695B6570-ACDC-4A8E-8545-26EA7FC1D162" />
<Feature ID="00BFEA71-4EA5-48D4-A4AD-7EA5C011ABE5" />
<Feature ID="00BFEA71-E717-4E80-DEAF-D0C71B360101" />
Adding Content Types to a Provisioned Site
You can add content types to a provisioned site through the Windows SharePoint Services object model.
To add a content type to a provisioned site
Use the Add method to add the SPContentType object to the site content type collection.