For all intents and purposes, the question is kind of meaningless - you cannot take 310-051. (It's been retired.)
The major difference, though to answer the question, is the targeted version of Java Enterprise Edition. -051 targetted J2EE 1.2, with early versions of EJB and similar technologies. -052 targets Java EE 5, with EJB3. The syllabus is on Sun's website.
Theodore Jonathan Casser
SCJP/SCSNI/SCBCD/SCWCD/SCDJWS/SCMAD/SCEA/MCTS/MCPD... and so many more letters than you can shake a stick at!
I would like to try SCEA certification. So i would like to begin studying but i have seen that the content of the first part has changed. Which books could i use to begin? Now There aren't new books again covering the last topic. Thanks dz