IF YOU ARE USING XP:
1) Double-click open the ZIP you downloaded
2) Click on Extract .... see pic
3) Click on Browse in the popup window
4) Expand to find your UI directory
C:/Program Files/Sony/EverQuest 2/UI is default .. then click Okay
5) Add in name of directory you want to use "myUI" is the example Some UI mod's include the main UI folder inside the zip, so its really situational.