Do you mean the rotation-equipped Nova? It's more of an accidentally canon ship. During an early battle in the E-M war (as seen in the ITB movie), a wave of Minbari War Cruisers are seen torching a group of EA capital ships. If you don't look too closely, you might think that they're just Nova class, but a more detailed inspection would reveal that all are rotation-equipped. The official answer, is that they were an accident of CGI, and were in fact Omegas, but as far as the show's timeline is concerned, they can't be, since that class wasn't commissioned until after the war. The compromise by fans was to declare that these were a group (and the only group) of experimental Nova designs intended for long-duration spaceflight, equipped with rotational sections. The idea would then be that the Nova-X was used as the basis for the Omega design. I do recall reading however, about a prototype ship with similar description to the Nova-X, I believe called Orion, but it was to have been designed after the war, and was quickly dropped in favor of the much better Omega. I think I may have read it on B5 Tech a few years ago. I don't think its there anymore.
BTW, there are some "reference images" in the link terran_emperor posted. A link within the ship description will take you there, but its quite hard to make it out from the images. Take it from me though, I've got the movie and I've seen the CGI blunder for myself. Not much to go by, so its a bit of a creative blank slate, unless someone else has made some fan models or specs. I wouldn't use the model image from B5 Tech, as its just an omega. I'd probably do a simple Nova with the rotational section, and perhaps a few aft-firing guns near the engines like on the Omega... just my take.
