[Br@nkoR]

Još sinoć počeo da pišem, pa videh da je problem samo centriranje.
Nešto na brzinu, moglo bi ovo i drugačije,
javascript:

$(function() {
  var slideshow = $('#slideshow'),
      content = $('#content');
  function resizeCallback() {
    slideshow.css({
      'margin-left': ((content.width() - slideshow.width())/2) + 'px'
    });
  }
  resizeCallback();
  $(window).on('resize', resizeCallback);
  
  $('.slide_block:even').addClass('not-active');
  slideshow.on('click', '.not-active a', function(e) {
    e.preventDefault();
  }).on('mouseover', '.not-active', function(e) {
    var elem = $(e.currentTarget);
    if(!elem.hasClass('slide_block')) {
      elem = elem.parentsUntil('.slide_block');   
    }
    elem.removeClass('not-active');
    $('.slide_block').not(elem).addClass('not-active');
    switch(elem.attr('id')) {
      case 'block1':
        var margineLeft = (content.width() - 1000)/2;
      break;
      case 'block2':
        var margineLeft = (content.width() - slideshow.width())/2;
      break;
      case 'block3':
        var margineLeft = (content.width() - slideshow.width())/2 - 1000;
      break;
    }
    slideshow.stop().animate({
      'margin-left': margineLeft + 'px'
    }, 1300);
  });
});

css:

.not-active {
  filter: alpha(opacity=30);
       -khtml-opacity: .30;
         -moz-opacity: .30;
              opacity: .30;
}