No, you don't need to register with RealtyTrac in order to use Trulia. The Trulia search engine, Stats & Trend pages, Heat Maps and Trulia Voices community are all available to you absolutely free of charge. RealtyTrac merely supplies us with the foreclosure listings included in our search results, and if you'd like information about those listing in addition to what we provide, you can set up an account with RealtyTrac. If you are interested in doing so, it's worth noting that you can setup a 7-day free trial and test our there service before you subscribe to it.
Please let us know if you have any other questions about this, or any of the other offerings on our site.