Today's the day that KMEG of Sioux City, Iowa, one of the few CBS stations to refuse to broadcast "Late Show With David Letterman" a year ago, finally joins the fold and adds "Late Show" to its schedule. No word yet on whether Mr. Letterman will relocate its Top 10 "home office," which it chose as Sioux City specifically to tweak that station for its lack of cooperation. But since we're not in Sioux City, that's more a trivia note than a programming note. For a programming note, try this: Tonight Fox follows a prime-time showing of "The X-Men" with a repeat of "The X-Files." In the history of television, this is a first: Two different X- series presented back to back. Tonight on Fox,
* "Mighty Morphin Power Rangers" (8 p.m.-8:30 p.m., WBFF, Channel 45) -- Tonight's show includes a changing of the bad-guy guard: Rita Repulsa has her role (and her body) diminished by Lord Zedd, who replaces her with a new lead villain: Pirhantishead. Fox.
* "The X-Men" (8:30 p.m.-9 p.m., WBFF, Channel 45) -- This new prime-time episode takes its plot from recent issues of the "X-Men" comic, with Wolverine forced to do battle with his former lover. That comic-book plot took six months. This must be the condensed version. Fox.
* "The X-Files" (9 p.m.-10 p.m., WBFF, Channel 45) -- Why are scientists, working on a top-secret aeronautics project, suddenly and horribly dying? What, if anything, does this have to do with UFOs? In this case, if U tune in, U Find Out. Fox repeat.
* "20/20" (10 p.m.-11 p.m., WJZ, Channel 13) -- Tom Jarriel reports tonight on a cop turned robber, but a man whose motive and daytime occupation were equally unusual: He was a cop, trying to raise money for his immobilized son's long-term health care. ABC.
* "Picket Fences" (10 p.m.-11 p.m., WBAL, Channel 11) -- The chemistry in this episode between guest star Della Reese and supporting player Adam Wylie (who plays Zachary, Sheriff Brock's younger son) is magnificent to watch -- and Ms. Reese, as a visiting blues singer, is, as always, wonderful to hear. CBS repeat.
* "Rebel Highway: Confessions of a Sorority Girl" (10 p.m.-11:30 p.m., Showtime) -- Jamie Luner heats up the screen, and eats up the scenery, as a bad girl terrorizing everyone at a '50s sorority. Alyssa Milano is co-star, but Ms. Luner gets all the good scenes.