Well, I'll try to explain them and see if it helps:
1. JAX-RPC enables
Java developers to
develop SOAP based interoperable web services. Its provides a way so that u can call services on other machines like RPC does.Its just a specification and an API and doesn't provide any implementation. Vendors are supposed to provide their own implementation.
2. SAAJ provides a way of creating SOAP envelopes (w or w/o attachments) which can be then sent across any transport. Jax-Rpc uses soap envelopes created by SAAJ. Again it is a specification and provides APIs but no implementation.
3. Apache-Axis is open source soap engine and provides implementation of both Jax-Rpc and Saaj. Its 1.2 version is going to be released sometime in coming weeks.
4. Apache SOAP is again a soap engine, Axis has evolved from apache soap and not much development goes in apache soap, so if u r starting new begin with Axis.
5. Not too sure about Sun's toolkit. Guess its just a reference implementation of the standards.
Ashutosh