I couldn't find one myself, and I guess Netscape did not write or replaced the 4.0 Release Notes.
As for the dynamic HTML implements, the best resource is the "archived section" of DevEdge
http://devedge.netscape.com/
Another good source about dynamic HTML is Danny Goodman's
Dynamic HTML: The Definitive Reference. (publisher O'Reilly) If you are looking for NS 2.x, 3.x, 4.x I would recommend you getting the first edition (1998); second edition (2002) is empharise on the standards and the new NS6/7 and IE 5+.
Since I myself have coded HTML + JavaScript since NS3, I guess I could write a short guide about the Dynamic HTML in Netscape. Still have all those printouts 
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