UAC (User Account Control) is complicate as I disussed before. Even you are a "Administrators" (Yes~~ it has 's', in Vista you only have one "Administrator" but much "Administrators"), you can not register the COM component. There is a way to tell you how to work it out!!
Such you can register your COM component, or you can use "Administrator" account (it will be disable by default, just go to "Manage-->Local Users and Groups--> Users" to open it.