The IRequest::get_QueryString method retrieves the QueryString collection of the Request object.
HRESULT get_QueryString(
IRequestDictionary ** ppDictReturn // pointer to an
// IRequestDictionary interface
// pointer that receives the
// QueryString collection
);
You can iterate through the QueryString collection with the IRequestDictionary::get__NewEnum, or you can retrieve a specific QueryString value with the IRequestDictionary::get_Item method.