You don't have to list your property with an agent for it to appear on Trulia (though Trulia believes agents are a very important part of real estate transactions and bring a lot of experience and expertise to the table).
All you need to have is a Web page that we can index. The easiest and fastest route is to use a service like http://www.postlets.com which lets you create and syndicate a real estate listing really quickly. Trulia has a data relationship with Postlets, so your postlets listing should appear on Trulia quickly.
Also be aware that all disclosure and fair housing laws apply to you as well.