Web site information architecture is an additional skill web designers may not have that you may need to outsource for.
Information architecture is tied to usability testing and how humans search, sort, classify and order things. This is not the same as site architecture that SEO’s use in their work.
Shari Thurow describes what information architecture is for web design, why its so important to design and how it relates to user centered design. She offers logical examples and a warning about basing design decision on search engine algorithms.