David Letterman gives Regis Philbin a sneak peek at some of what he has in store for Oprah. (AP photo)

Tonight is the night: The Queen of Daytime visits the King of Late Night. Oprah Winfrey makes her historic debut on Late Show With David Letterman. (11:35 p.m. on OMNI1 and CBS). But will it float?

Letterman and Winfrey have supposedly been feuding since her last of two late night visits (to Letterman's old NBC show) 16 1/2 years ago. Twice was enough she told Time magazine in 2003. "Both times I was sort of like the butt of his jokes," she said. "I felt completely uncomfortable sitting in that chair, and I vowed I would not ever put myself in that position again."

You could hardly blame her. Although Letterman could always say he was just kidding, he constantly lampooned Winfrey, goofing on her up and down weight, her book club, her showy "favourite things" giveaways, her perpetual O magazine cover shots (Top 10 Articles In Oprah's New Magazine: 4. "My Love Affair With Oprah," By Oprah). In late 2001 and early 2002, he kept an "Oprah Log," goofing on how she still had not called to invite him on her show. The day after Winfrey handed out new Pontiacs to her entire studio audience, Letterman doled out new car air fresheners.

They are as opposite as men and women, black and white, irony and empathy. Winfrey the touchy-feely hugger, Letterman who can't hug anybody. Winfrey who promotes literacy, Letterman who promotes stupid human tricks.

Still, these two are more similar than you'd think. Neither will commit to their long time mates. Both have had Tom Cruise jump on their couch. Okay I guess just those two things.

Still, you could sense a thaw in the air. For two years, Oprah's pal (and first husband, according to Dave) Dr. Phil McGraw has been one of Letterman's most frequent guests, razzing the talk show host about his Oprah-phobia. Letterman seemed to wince at the needling but kept inviting him back, suggesting McGraw could host or referee the "Super Bowl of Love," Letterman's name for any eventual thaw in their feud.

Now it is actually happening. Is it because Winfrey thinks Dave has softened up some now that he's a heart surgery survivor and a doting dad? (She sent him a tub of books when Harry was born, all with "Harry Book Club" stickers on them.) Is it because Letterman has been groveling like crazy lately, mooning over a giant poster of Winfrey he unfurls behind his desk each night for the past two weeks?

Naw, it's strictly business, baby. Both Letterman and Winfrey work for Viacom, the media conglomerate that owns both CBS and syndicator King World. Winfrey has a Broadway play to sell, The Color Purple, which is having its red carpet premiere on the same night just up the street from Letterman's Ed Sullivan Theatre. In other words, she was going to be in the 'hood anyway, had already fasted into her dress and with a million bucks invested in the play, what the heck.

Winfrey's brand new 20th Anniversary Boxed Set DVD will also likely get a little screen time on tonight's Letterman. Will stagehands Pat and Kenny also come out and read Oprah transcripts (a hilarious nerve-smacker Letterman has pounded for years)? Only if Winfrey thinks it is funny.

Look for dozens of roses, Letterman on his knees, nothing but kindness from Dave. Look for Dr. Phil holding Dave's arms as Winfrey punches him in the stomach -- or some sort of wedding ceremony. Look for the Super Bowl of Love.

That's if she shows. If she ditches, look for Dave to heave those Oprah DVDs off the roof of the Sullivan theatre or "Can A Man In A Bear Suit Get In To The Color Purple?"

Memorable Letterman guests

1987: Sonny & Cher (prodded into a touching rendition of I Got You Babe by the host)

1994: Cigar-chompin' Madonna uses the F-word 13 times

1995: Drew Barrymore flashes Letterman in April on his 46th birthday

1997: Farrah Fawcett's bizarre behaviour leads to rumours of drug abuse

2004: Courtney Love tries to outdo Barrymore by repeatedly flashing a less than amused Letterman

2005: Phone tosser Russell Crowe's confession that he got out of jail thanks to "friends" in the NYPD led to charges

Feuds a long tradition in TV

Think things have been touchy between Dave and Oprah? The Letterman/Winfrey feud is part showbiz legend, part showbiz ballyhoo. Sure, feeling have been hurt, but Letterman has also milked the rift for laughs. It's one of his show's surest gags, right up there with George Bush is an idiot and the New York Mets suck.

Real showbiz feuds are as old as late night talk shows themselves. Letterman/Leno has been stewing ever since Jay Leno got the Tonight Show gig over Letterman when Johnny Carson retired in 1992. Leno, who used to be a regular on Letterman's old NBC hour, recently called for an end to the hostilities. "I owe my career to Dave," he said in 2003. "It has been 11 years and everybody's rich, everybody's successful. Come on."

Easy for him to say. It's also been 11 years since Letterman has come close to Leno in the ratings.

Going further back, Johnny Carson reportedly never spoke to Joan Rivers again after the comedienne abandoned her Tonight Show guest host gig for her own Fox talker in 1986. (It flopped.)

When Jack Paar hosted The Tonight Show in the late '50s, early '60s, he had a bitter feud with TV showman Ed Sullivan. Paar complained (sometimes on air) about how Sullivan scooped the best guest stars by paying them a higher fee.

A truce was called in 1964 when The Beatles were booked on Sullivan. Paar's teenage daughter Randy was so anxious for tickets she pleaded with her father to end his feud, suggesting it was the Christian thing to do.

Paar told the story on the air right before the Sullivan show. Within 24 hours, four tickets to The Beatles came from Ed Sullivan. Randy took future U.S. president Richard Nixon's two daughters to the show. As Paar used to say, "I kid you not."