just downloaded it and had a look. The transparency maps don't export; not insurmountable, it would be simple enough to make your own from the colour map.
I do think this is probably an indication that eon don't wish people to export from the free version.
More telling is the fact that all the textures are watermarked with the eon logo and the word eon through them
Given all that, it seems pretty clear that the makers and vendors of this software do not intend it to be used in the way you describe. Granted they have not expressly forbidden it (unless of course you use the results commercially, in which case you would be in violation of the agreement), but I think that "not totally unethical" is pushing it. Vue is an amazing piece of work that must have cost a fortune to develop. I wish I could afford it, but I can't, but I don't think that's an excuse for cheating on the developers
just my two pence worth
