Your INF file must create two registry keys, one that defines the extension's globally unique identifier (GUID), and the other that declares the GUID as a control-panel extension. The appropriate part of your INF file should look like this:
[DriverPagesAddReg]
HKEY_CLASSES_ROOT,"CLSID\{Your GUID}\InProcServer32",,,yourdll
HKLM,"Software\Microsoft\Windows\CurrentVersion\Controls Folder
\ControlPanel\shellex\PropertySheetHandlers\DriverPages",,,
"{Your GUID}"
You should always use the OLE2 utility, GUIDGEN.EXE, to produce a new GUID.
For more information about INF files, see Device Information Files in the DDK.