K3B problem
 

In Arch 0.7.2 (gimmick), I have installed k3b using pacman.
When I start k3b it says it is to be used with root's privileges.
I tried to use the setup option but don't know how to proceed further.

You should just need to run k3b setup, click apply and that's it.
You may need to run k3b as root for the setup to work but then you'll only need to run it as a regular user.