I remember many years ago this game came with its own UI building tool. I don't seem to have it in my latest install of the game though. The only reference I can find to it is a 6 year old update available on EQ2Interface.com. http://www.eq2interface.com/forums/faq.php?faq=uibuilder It would be neat to have the latest copy of this available from DBG.
Yeah, unfortunately that's the last version that seems to be available anywhere. I have to imagine that the UI has been modified so drastically since its release though that there must be a newer version that the devs use. It would be nice for them to make it available again.
The UI files are all now XML format. You most likely get some advice on how to build EQ2 UI's, if that's your aim, over at http://www.eq2interface.com/