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 QuerySting collection with the IRequestDictionary::get__NewEnum, or you can retrieve a specific QueryString value with the IRequestDictionary::get_Item method.