GOOD MORNING: There’s no question about the ratings World Championship Wrestling’s “Monday Night Nitro Live” on TNT has been getting — but there’s a large question as to why Jay Leno would get himself (physically) involved with the likes of Hulk Hogan and fellow wrestler Eric Bischoff (who also co-host the show’s talk seg). I asked Leno why he and his wrestling partner Diamond Dallas Page will step into a ring in Sturgis, S.D. — site of a 200,000-biker rally — for a pay-per-view wrestling match vs. Hogan and Bischoff. (The match is preceded by a 35-min. concert by Travis Tritt.) Wednesday, Leno told me he was mad at Hogan and Bischoff because, he claimed, “they were taking my jokes and even copying my set” on their “Monday Nitro” show. “I thought I should fight back.” I told him I didn’t think “fight” was such a good idea. But Leno said, “I think I’ll be OK.” He won’t even wear any protective padding, he further claimed. Of course, Leno is doing it all for charity (and publicity). Meanwhile, South Dakota’s Sturgis is gearing up for the arrival of the 200,000 bikers, and the wrestling match (building a ring and bleachers for 15,000 on the town’s main street). The pay-per-view moguls are expecting a huge viewership; they point out that in 1997, World Championshp Wrestling had four of the top PPV grosses of the year. And with the appearance of Leno, surrounded by fellow bikers, they expect another blockbuster. Anyhow, the event gives Leno a nightly breather from political humor, though he admits, “Thank God for the news — the humor from it writes itself.” As do the laughs about this upcoming match. Leno is expected back on his (regular) show Monday following Saturday’s outcome. Leno usually plays club dates on weekends and doesn’t take vacations. Until now.I’VE LEARNED NOT TO BE BITTER,” Debbie Reynolds said as her Las Vegas hotel sold at auction Wednesday for 9 million — to the World Wrestling Federation. Whereupon Kenny Kerr, headlining at Reynolds’ hotel, offered to “mud-wrestle Hulk Hogan.” Reynolds added, “It’s just another step in life I’ve had to get through. And I’ve always had my work and I still do.” She recently completed two TV movies, “Halloween Town” and “A Christmas Wish.” As for commercial ventures, she philosophically added, “I’ve learned what not to do — I was gullible,” she said of past financial (and personal) partners. She thanks her son Todd Fisher, “who has been at my side constantly and has been a tower of strength.” Daughter Carrie had been an original investor in the hotel, but Debbie says, “I paid her back.” Before the hotel went up for sale, Reynolds moved her Hollywood Museum artifacts from the hotel and placed them in storage. The Museum is a non-profit entity and she has several offers for a new home for it. Debbie, Carrie and Todd receive the AFI Associates’ Platinum Circle Award, “acknowledging families whose creative contributions have enhanced the entertainment industry” Sept. 17 at the BevWilshire … From a more pleasant site, her home in the south of France, Joan Collins happily reports she is going back to work in a feature, which is definitely “a change of pace.” The movie, “The Clandestine Marriage,” is an 18th century period comedy costarring Nigel Hawthorne and directed by Christopher Miles for Portman Films. The pic will be shot in Gloucestshire this fall. In the interim she’s completing a book, “My Friends’ Secrets,” a followup to her book, “My Secrets.” “I’ve interviewed 22 of my best friends,” she says, and will report their “secrets” of beauty, health and philosophy. “They’re all between the ages of 40-75,” said Collins and include Ivana Trump, Diahann Carroll, Shirley MacLaine, Stefanie Powers, Jerry Hall, Shakira Caine, etc. Collins was anxious to hear more about the Robert Evans-Catherine Oxenberg marriage/annulment. “She (Oxenberg) was one of my daughters in ‘Dynasty,’ ” Collins reminded. “And she married a prince” — in the series. Meanwhile Collins and Robin Hurstone are celebrating 10 years of togetherness. Marriage? “Why spoil it?” she asks/says.