There is no demo version. The software is exactly the same, the only difference is if you have an interface or not. If it is not connected it says it's in demo mode. This is how I work all the time preparing the shows offline on my desktop, no interface and when I have finished I copy the show to a USB stick and then transfer to my "Show" laptop.
You should install the software first before connecting the interface as it needs drivers installed before it can be used. See the videos her http://www.daslight.com/tutorials/
I suggest doing this if you are using teh latest software from the website.
Un-install DVC2 and DVC1 if you have it installed. All you shows will be OK.
Then un-install any daslight drivers.
Get the latest drivers from the website and install them.
Then install the DVC2 software from the website.
Apparently the older drivers will only work with the older software and the newer drivers will only work with the newer software. Not sure of the date of change.