what is the difference between preliminary hearing and pre-trail hearing or are they the same and what do they intell

A preliminary hearing is a hearing held in the local justice court to determine whether there is reasonable cause to belief that a defendant committed a felony and should be held for the action of the Grand Jury. 

A pre-trial hearing is just what the name implies.  It is a hearing held prior to trial, usually to determine whether certain evidence (a statement, identification procedure, physical evidence, etc.) will be admissible at a trial.