$("form#new_group #group_name").live("keyup", function() {
  var $input = $(this), name = $input.val(),
    $sub_input = $("#group_subdomain"), subdomain;
  
  subdomain = name.toLowerCase()
    .replace(/[^a-z0-9]/g, "-")
    .replace(/-{2,}/g, "-")
    .replace(/(^-|-$)/g, "");
    
  $sub_input.val(subdomain);
});