There was a great UI building tool for DAoC that I used to use called daoced. It had a full preview with sample data entered for you, and all your changes were displayed in realtime.
This is probably why I haven't gotten into EQ2 UI editing yet - the UIBuilder program makes almost zero sense at first glance, other than the XML tree it displays.
So I agree with TyeJae that there needs to be a better tool than having to load the game to see UI elements
