Try using the version located here...
http://www.wowinterface.com/download...UIRelease.html . It's the current release version which is also the stable one for live servers. The only "beta" version is the one being setup for the PTR. The "Dev" version is actually older than the "Release" by the version numbers.
Some people have reported that when they initially log into the game, their screens look like that also and ended up being resolved by doing "/nui rl" or completely relogging also.
For most other things, like the slash commands etc, check here in the nUI forums under the FAQ section. You'll find alot of information there. If it's not covered somewhere in those listings, by all means ask, usually someone knows
