The Dropdownlist Items can be added through codebehind...But, one main point is
you cant add the items in page load.
Ex: ddl_type.Items.Insert(0,"Create New");
It can be added on Page_PreRenderComplete stage of the Page Life Cycle.
The Items Will Be Bounded in this stage of Page Life Cycle.
Reason: The Page_PreRenderComplete() here the datasource id will be appended to the required controls.
For Detailed Description Go through this link.
To Open new page Enable the Autopostback = true and in code behind on dropdownlist selected index change.
All The Best