By Amy Argetsinger and Roxanne Roberts
Thursday, May 10, 2007 12:52 AM

A mysterious parcel was delivered to The Reliable Source yesterday, purporting to be a ransom demand for the $1,500 sculpture by local glass artist Tim Tate that went missing from the Artomatic show.

As we reported two weeks ago, the rocket-ship-looking doodad -- dubbed "The Rapture," as it happens -- vanished from its installation at the Crystal City art show around the time of the raucous opening-night party April 13. That's believed to be the last time anyone saw a trace of it . . . until yesterday.

The package, shipped by overnight mail and addressed to us, bore the cryptic name "The Collector," with a nonexistent return address at "2300 Constitution Avenue NW." We gingerly opened it under a ventilation hood, anticipating . . . well, something awful. Instead, we found:

• A photo of what appears to be Tate's rocket ship, posed in front of the front page of Tuesday's Post, with a toy gun aimed at it.
• A note demanding that Tate place "$10,000 monopoly (unmarked) in a paper bag and drop it in the lap of the Albert Einstein statue in Potomac Park" next week.
• A piece of flame-colored glass that appears to be the top of Tate's sculpture.

Thus far The Post has decided not to involve the police. We called Tate, who asked us to read the note a second time before his coughing fit of laughter subsided. Is this a publicity stunt? "I am not involved in any of this," he said.

Can he amass that amount of Monopoly money by next week? "I bet I could. I'll raid my nephews' and nieces' board games." And will he accede to the kidnapper's demands?

"Are you kidding? I wouldn't miss this for the world. I'm getting my rocket back, man."

Queen Elizabeth and Prince Philip spent the final hours of their U.S. visit Tuesday at a private black-tie dinner for 104 guests at the British Embassy. The evening was designed to be more casual than Monday's white-tie bash at the White House: No tiaras, and women were asked to wear short cocktail dresses (Hillary Clinton was the only one who opted for pants). The tables were named for Kentucky Derby winners; the queen was seated at "Smarty Jones."

The dinner honored President Bush and Laura Bush; the guest list included members of his cabinet and political and cultural VIPs who British Ambassador Sir David Manning hoped might amuse the queen: George H.W. Bush and Barbara Bush, Nancy Reagan (one of the lucky repeat customers, having attended the White House dinner the night before), Alan Greenspan, Vernon Jordan, Susan Eisenhower, Maryland Gov. Martin O'Malley, D.C. Mayor Adrian Fenty, and Sens. John Warner, Dianne Feinstein and Mel Martinez. British film director Michael Apted, the Shakespeare Theatre's Michael Kahn, pianist Van Cliburn, architect Leo Daly, and journalists Jim Hoagland, Andrea Mitchell and Tom Friedman also made the cut.

The 81-year-old queen got the last word when she gently teased President Bush for his arrival ceremony gaffe. She raised her glass to him and said (with that perfect accent of hers), "I wondered whether I should start this toast by saying, 'When I was here in 1776 . . .' " -- and got the biggest laugh of the entire trip.

• Ron Jeremy at the Tantra Lounge at Indebleu late Tuesday night. The adult-movie star debated pornography with evangelist Craig Gross at the University of Maryland earlier that night, then made a midnight appearance at the downtown bar to sign his memoir, "The Hardest (Working) Man in Showbiz," and autograph the bosoms of female fans.
• Rudy Giuliani, accompanied by a three-man security detail, perched on a stool at K Street Bagel Tuesday afternoon. The Republican presidential hopeful (who addressed the Heritage Foundation Monday night) took a coffee break with an unidentified man.
• Howie Mandel, in town to talk about children's mental health, with 10 guests at Blue Duck Tavern's private chef's table Monday night. The "Deal or No Deal" host, in black pants and a white button-down shirt, ate roasted chicken.