Ton Stegeman [MVP] wrote a wonderful article about how to create a custom sharepoint page.
However, when you are searching for the hidden
It is NOT in the sharepoint.dll. You must add a new reference to the Microsoft.SharePoint.ApplicationPages.dll. You can find this dll here:
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\CONFIG\BIN\Microsoft.SharePoint.ApplicationPages.dll
nice to know not?