Integration with the RDF module
Themes will work with the RDF module if they use the proper attributes variables. 

If you are generating HTML outside of the core theming (which seems unusual) system you will need to get this information yourself. The RDF mapping api is quite well documented. Essentially there is a mapping between fields and RDF. So a title field could have a mapping of dc:title. 

In summary


rdf_get_namespaces() will show the namespaces that need to be included in your document.
rdf_mapping_load() will show the rdf mappings for an entity type.


You can then add rdfa markup to the fields as you output them. 

edit

If you are using standard theme functions, then so long as you stick to the D7 guidelines all of the RDF magic should be done for you. Specifically make sure that you use $attributes $title_attributes and $content_attributes.

If you want to know how to define RDF mappings, then please ask more questions.