Hi,
I'm not good with copyright laws, but maybe this story (preceded by a few comments) could help.
First, the assumption that if you don't make money off of it, it's legal, is false (I'm afraid). There is such a thing as fair use of copyrighted material (see the annotated EV bible for a taste), like quoting and stuff, but it's limited.
Basically, everything ST is copyrighted. It's not Data, it's Data. It's not Jean-Luc Picard, it's Jean-Luc Picard. You get the idea. Ditto every Enterprise, ship, and most junk they made toys or memorabilia out of.
Now, the little story. I worked as an office clerc for a big business a few years back (I won't name 'em, but I can tell you it was AT&T; kinda big...), and one factory in Montreal (where I worked) wanted to do an open house. They had decided on a variety of gifts for adults and kids. One gift was a coloring book. Someone had simply re-drawn characters of Disney, plus Bugs Bunny and Yuppie, the Mtl Expos (MLB) mascot. We later checked for copyright laws with the Expos and they said we couldn't use the big fuzy orange ball they call a mascot. So we took it out. We later asked a graphics expert (he did our posters and stuff) what he thought. He said: "Even if you're not making money with it, drop the coloring book idea." We asked him if Disney and Warner would sue. He told us, "If they ever hear about it, expect fees starting at 100 grans." For starters.
I wish you all the best of luck, sir, with your ST plug-in. I'd do it myself if I had the graphic skills... Go ahead, ask Paramount about it. That would be your safest bet. Even if you're not making money off of that plug, Axis could gain popularity with a ST plug. And Paramount would feel you gained that popularity off of their product. I'd ask them. Or I'd publish the plug under another name...
Hope this helps (and sorry for the length),
Gorizo
(soon to be another registered user of EV. Let me get a job first...)