Async requests using Win32

I'm just getting to grips to www-lib so excuse any daftness in this   

I making a Windows application and building it up slowly so I get a   
better idea of what each of the components of www-lib does. My   
initialisation is simply this:

HTLibInit("TestApp", "1.0");
HTTransport_add("buffered_tcp", HT_TP_SINGLE, HTReader_new,   
HTProtocol_add("http", "buffered_tcp", HTTP_PORT, YES, HTLoadHTTP, NULL);

Later on I retrieve a URL into memory with the following:

HTRequest * request = HTRequest_new();
HTRequest_setOutputFormat(request, WWW_SOURCE);
HTRequest_setPreemptive(request, YES);
HTChunk * chunk = HTLoadToChunk (szURL, request);

At present, this is synchronous (blocking) - can someone give me a few   
pointers as to what I need to do to get it working asynchronously?

Paul Dixon