https://www.oreilly.com/tim/herbert/

Edit: I see Tim O'Reilly was the editor of the "Maker of Dune" book mentioned here also.

I used to have a copy but sold it at some point. Apparently it's hard to find now, given the very high price.

Update: The entire book is in the Internet Archive! https://archive.org/details/the-maker-of-dune-insights-of-a-...