For anyone yet to try NX (and I commend it to anyone not willing/able to pay for CS3, not just Nikon users), it is necesasary to use the correct regional site, (corresonding to where a Nikon product is registered) and regional version of NX to smooth the course.

Thus although the US site http://support.nikontech.com is the richest source for tutorials and Q&A, downloading upgrades from it causes trouble with an EU registration no or NX product key http://nikoneurope-en.custhelp.com (probably the same with FarEast).

The EU/US versions are slightly different, so even for free trial, start with the right one. For EU 1.3 trial (or upgrade from 1.2) you need a product registered, which can just be any old Nikkor lens.

Lastly for mac users, use Disk Utility>repair permissions before all installations.