shell extension: How to use IThumbnailProvider in Windows vista!

I will implement IThumbnailProvider in my ATL project. And in the rgs file,
i set the key value{MY GUID} in
HKEY_CLASSES_ROOT\.xxx\shellex\{e357fccd-a995-4576-b01f-234630154e96}, and I
implemented IInitializeWithStream::Initialize() and
IThumbnailProvider::GetThumbnail().
I set a breakpoint in Initialize(), but it seemed that explorer.exe had
never called Initialize().

Am I missing something?


Thanks!