On the Road With Charles and Diana: The Samsonite Couple arrived in Melbourne yesterday as part of a 10-day visit to the Australian state of Victoria to mark its 150th anniversary. And then they'll be coming here for the whirlwind receptions, parties and dinners before flying down to Palm Beach, Fla., for a bit of polo and a fancy fundraiser. Only then will they wing back to London to see if chubby cheeks Prince William and Little Hank have been doing their homework studying photographs of mommy and daddy so they won't be frightened when the unfamiliar couple comes in for their welcome back kiss.

There was one minor breach of royal etiquette at the Melbourne airport when one man, excited to see real royalty, actually bent forward and kissed Diana's hand. Fortunately, the princess accepted the tribute in good humor. Had it been HRH the queen, the man would probably have been seared where he stood by one of Elizabeth's withering glares.

And as for the Palm Beach party that Armand Hammer is throwing as a fundraiser for the United World Colleges, there doesn't seem to be a great clamoring to attend. Even with Charles and Diana dancing the night away, some of the big money types are balking. The Miami Herald reported yesterday that at the $10,000-per-couple price for some tables and $50,000 a couple for good tables, Gregg Dodge, wife of the late auto mogul Horace Dodge, said she will be unable to attend. "That's the day I have to have my legs waxed." Things are Jumping at the Horse Show

Wealthy Dallas real estate baron Charles J. Ziff believes young people don't have to be rich to be part of the horsy set. That doesn't often go down well with the older money types, who feel that if you're not born to the bloodlines, you can never truly belong. Ziff is the chief backer of the U.S. Equestrian Education Foundation, which offers scholarships for young horsemen and horsewomen. And who should win the $10,000 U.S. Junior Grand Prix League Award? Ziff's son, David Ziff, 13, whose horse won the most money during a five-part jumping series over the past year. The young man of course declined, but he also came in second for the $10,000 Senator's Cup -- sponsored by his father's park -- when he was riding his father's gelding.

Other horse show notes: Playing Games, a 9-year-old chestnut gelding owned by actors Paul Newman and his wife Joanne Woodward, was named reserve champion in the show's large junior hunter's division . . . And a love story: David Wade, 24, and Maureen Cane, 21, went to last year's horse show on a first date. Things progressed smoothly from there and on the one-year anniversary of that date Saturday, they were in the audience when the giant Cap Centre screen announced: "Maureen, I love you. Will you marry me? Dave." An old-fashioned type, Wade already had the permission of Cane's father. She cried and said yes. That was announced on the screen, too. Wade said as soon as he sells a horse, he will buy her a ring. Some of the horsemen were shocked. There are those who would turn that trade around. End Notes

Suspicions about the death of Marilyn Monroe are heating up in court. Sam Cordova, the foreman of a Los Angeles grand jury, says he will ask for a special investigator to begin a probe into the circumstances of the actress' 1962 death, which was ruled a suicide . . .

When Cher comes to town this week to receive one of the Lab School of Washington Outstanding Learning Disabled Achievers awards, she is coming in style. The singer-actress, who has made more worst-dressed lists than best-dressed lists, had aides call ahead to request two cars -- one for her and one for her luggage. Cher's award at the black tie dinner-dance at Hecht's new Metro Center store will be presented by House Speaker Tip O'Neill. And the approximately 700 people expected for the dinner on the store's fourth floor will not all be treated equally. Those paying $500 a ticket will be seated in "Better Dresses," while those paying $150 will have to settle for dining in "Sportswear" . . .

E.B. White, whose magical typewriter was silenced when he died Oct. 1, was memorialized in Blue Hill, Maine, Saturday by his longtime friend J. Russell Wiggins. Wiggins, a former Washington Post editor and U.S. ambassador to the United Nations, said White possessed "the two chief qualities of a writer: he had something to say and he knew how to say it . . . he spoke for the cities and that made him the voice of The New Yorker and, with equal authority, he spoke for rural America" . . .