Please provide more information. Which EPiServer version?
Are you talking about the "Manage shortcut" dialog from the Settings tab when editing a page in EPiServer 7?
What functionality is it that you want to copy - being able to link to an external URL with target options, or the validation that is used for the External Link field?
(For adding validation to properties, see http://www.david-tec.com/2012/06/EPiServer-7-Preview---Using-validation-attributes/)
How I can create a link similar to existing link on "External Link" add on to Configuration?