First make sure you are using the newest utility version, v3.1.3.5 (
link). Next drop a copy of the utility into the EverQuest II\BetaServer\UI\ folder and run it from there. It will figure out where the game folder is.
Note: On the Beta server EQ2MAP is not available yet, so when setting up DarqUI click
No for installing EQ2MAP. Also there are a couple of server messages that you'll want to look at after installing.
.