I've been scouring the internet for the better part of the past 6 months for version numbers and build numbers of WoW from before the public beta. I've managed to find a handful of photos from the very first press event that took place after the announcement in September 2001.
These photos were taken at a press event in February 2002, in France. The version number is unknown, but it features a Warcraft 3-like menu, much like a later build that was demonstrated at E3 in May of 2002.
I have more in the album that that's from - akspa420's Album: WoW Press Event 2002
Some of the earliest images are taken from whatever version this was, likely the internal pre-alpha without a version number. To the right is Shane Dabiri, who at the time was the Lead Producer of WoW. (see his linkedIn profile for his CV - http://www.linkedin.com/profile/pub/shane-dabiri)
Later on, during E3 2002, a similar build was shown, however the bottom bar was gone, and the action buttons were consolidated to a small block at the lower left side of the screen. By E3 2003, the UI had undergone further changes and was effectively fully developed - the default UI has changed very little from 2003.
I will be adding to this thread as my research continues into the history of WoW. So far, the photos and videos from 10+ years ago are hard to come by, but perhaps with appropriate petitioning and letter writing, I may be able to get more insight into how everything came together.