If you're having trouble even with the default UI, I would suggest deleting the default subdirectory/folder in the UI subdirectory/folder (Everquest II/UI/Default) and let the patcher pull a fresh set.
Then to get your custom UIs functioning, simply unzip the contents of the UI packages into newly created folders in your UI directory like Zonx stated. Refer to
this thread for step by step instructions on doing this.
The difference between the two settings files is resolution settings. You
can use any resolution you want, but those two files included will allow you to just 'plug and play' the UI (install it without any need to manually move the windows to desired locations).