Actually, sounds to me like a step in the NSN GR Downloads install was skipped. The installer script has two steps in it, one to create the new NSN tables and the other to copy over the downloads from the original download module tables to the NSN ones.
If you have not yet created any new downloads using NSN GR Downloads it is not too late to run that copy step.
Also, for the sitemap, make sure you are using kguske's NSN GR Downloads content replacement script.
BTW, I've been using NSN GR Downloads on RavenNuke and with Sitemap for a couple of years now.