Kennedy buffs rejoice: What's thought to be the biggest-ever cache of JFK and Jackie O memorabilia is heading to auction, including a racy letter from Jackie to Sen. Edward Kennedy's former wife, Joan, urging her to rein in her wandering hubby, a life preserver from jfk's sailboat Victura, and the former first lady's own 8-mm movie camera. We've noted auctions by Alexander Autographs before, but this one, online February 2425 at alexautographs.com, is really rich. Just consider the Jackie-to-Joan letter, worth an estimated $5,000 to $7,000. In the unsigned letter, Jackie tells Joan to take charge of the family and balk when Teddy spends too much time with his siblings or worse. "This is the 20th centurynot the 19th" she pens, "where little woman stayed home on a pedestal with the kids & her rosary." The best part is how the goods became public. Seems a former helper recovered the items from Joan's Cape Cod home and put them in storage. But she forgot to pay the bill; the stuff was auctioned off, and the top bidder is cashing in.