Ever wonder what a Vulcan looks like nude? Us neither, but obviously somebody has. Adults-only Star Trek books, magazines, and videos are doing boffo business at Trek conventions. Among the X-rated wares for sale: fanzines like X-Gen: An adult exploration into the universe of ”The Next Generation,” a 45-page collection of fan-written stories detailing acts of intergalactic perversion so shocking they’d make an Orion slave girl blush (”Data awoke to find his bedsheets floating inches above him ”); K/S, a series of underground Trek books featuring male homoerotic stories about Captain Kirk and Mr. Spock (all written, strangely enough, by female fans); and, for more visually oriented Trekkers, Sex Trek: The Next Penetration, a hard-core spoof you can also find in the X-rated section of video stores, in which Spock’s ears grow when he’s erotically aroused. Its most torrid scene: a Vulcan threesome. Va-va-va-voom!