Hi Anna Marie,
Posting a listing on Trulia is absolutely free! We do not charge for listing inclusion.
Please do keep in mind Trulia only shows listings that are currently represented by an agent or broker. If you have an agent, all you need to do is tell them about us and point them to the page I'm linking to below. They can fill out a simple form to tell us about themselves.
Follow this link, it will guide you to submit listings via a web crawl or an XML feed. If you don't have access to sumbit this way directly, or through your broker, you can also upload your lisitngs to Point2Agent using a form and they can upload to Trulia and other sites also.
Ann Marie, I see someone from Trulia has informed you about the Realtor listings on this site. Your profile doesn't show where you are, but I am involved in a nationwide Realtor referral network if you'd like my help