Auto-Negotiation is described in
IEEE Standard 802.3, 1998 Edition. "Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications." Chapter 21, 28, 34, and 37.
For a good introduction to Auto-Negotiation, see
Verschueren, Ben. "Auto-Negotiation Is Our Friend." University of New Hampshire Interoperability Lab. Available from Internet: http://www.iol.unh.edu/