names.insertElementAt( "Elaine", 2);
0: Amy 1: Bob 2: Elaine 3: Chris 4: Deb
As requested, "Elaine" is inserted at position 2 and all elements previously at position 2 and higher are moved up one to make room.
firstElement() and lastElement()
The firstElement() and lastElement() methods 
are sometimes useful.
They do what you imagine:
import java.util.* ;
class VectorEg
{
  public static void main ( String[] args)
  {
    Vector names = new Vector( 10 );
    names.addElement( "Amy" );    names.addElement( "Bob" );
    names.addElement( "Chris" );  names.addElement( "Deb" );
    System.out.println( names.firstElement() ); 
    System.out.println( names.lastElement() ); 
  }
}
The program prints out:
Amy Deb