In Texas, when is it necessary for police to obtain consent to search? Is there an online resource available?

In the state of Texas, do the police need consent to perform a personal search? What about a search of a vehicle? Under what cirstances is a warrant required? Is there an online source outlining any changes made as a result of Homeland Security that can be relied upon to be accurate and is in layman's terms? Has anyone contested the legality of pre-trial drug testing?