If you are a for sale by owner the post is not allowed, you can however try blogging about the property; if and when you do list with an agent he/she can post it for you, ask; or consider any flat fee realty company that feeds into the site.
Trulia does not post owner listed properties. Their are other sites that do, however. Most of them, I think, charge fee's to list with them. I would do some extensive research before I paid fee's to make sure the site I listed with will give you the exposure your looking for. If you have any other questions, don't hesitate to contact me directly!