Try searching for "structural equation modeling" on http://rseek.org. You'll find several helpful links, including links to several possible packages.
You might also check out the Task View for the social sciences, there's a section for structural equation modeling maybe a third of the way down. See http://cran.r-project.org/web/views/SocialSciences.html.
One package in particular you might find helpful is John Fox's cleverly named sem package.
http://cran.r-project.org/web/packages/sem/index.html