You can create your own property pages to customize the Microsoft Outlook Options dialog box (available through the Tools menu of the explorer and inspector windows) and the Properties dialog box for all folders.
A custom property page is an ActiveX control stored in a dynamic-link library (DLL) that implements the PropertyPage object and that’s installed as a COM add-in. This object provides the interface through which Outlook can query the property page about its status and inform the property page that the user has clicked the Apply or OK button.
Learn about adding custom property pages.