If you are looking to experiment with this piece of history, it is widely preserved in the community:

Windows Longhorn Build 4074 (idx02) 64-bit represents a critical milestone in the development of what eventually became Windows Vista

Include driver fixes and enable hidden features like out of the box.

By early 2004, the Longhorn project had become unmanageable. Developers were checking in code that broke the build almost daily, and the envisioned features—specifically WinFS—were causing severe performance issues and stability crashes. The famous "WinHEC 2004" build (4074) was the last major public showcase of the "pre-reset" vision.