You need to look into the MailItem object and the Application_NewMailEx event in the VBA help. The Application_NewMailEx event is fired every time you receive a message and it's parameter is a collection of the received messages. The MailItem object has the Subject and Body properties you're looking for.
Remember you will need to check the arriving message to determine if it is a MailItem or not before accessing the Subject and Body properties, or you may get a runtime error.

Good luck.
-EM