Ok, so the first problem is solved in that I hadn't realized that the converted files needed to be converted to VRML97. I'm now using this:
http://ovrt.nist.gov/v2_x3d.html
As a result I no longer get a little error box that simply says "(filename) failed to load". Now when I attempt to load any of the converted files the cursor changes into the loading icon and stays that way (I waited several minutes with the three files I tried before force-quitting Vizard). I'll send those files to
support@worldviz.com
As for using the UnrealEd-to-X3D converter, I haven't actually used it yet. For right now I'm just trying to get the sample files to run in Vizard so I can make sure its possible.