Making art isn't easy just ask the creators of Notting Hill. In the flick, to prove her love, a high-powered movie star (Julia Roberts) gives a bookseller (Hugh Grant) a rather lavish gift: La Mariee, a painting by Marc Chagall. Director Roger Michell says the work of a floating bride and a violin-playing goat was chosen because Chagall is a favorite of screenwriter Richard Curtis' and because the painting ''depicts a yearning for something that's lost.'' However, creating the faux Chagall and the one used in the film is a fake; some experts say the real canvas could be worth between $500,000 and $1 million proved nearly as difficult as deciphering Picasso. First ''we had to get permission from the painting's owners,'' says Michell. ''It was in a private collection in Japan.'' Then producer Duncan Kenworthy had to get clearance from the U.K.- based Design and Artists Copyright Society. And then, says Kenworthy, ''we had to agree to destroy it. They were concerned that if our fake was too good, it might float around the market and create problems.'' Thus, two months ago, Kenworthy tore the sham Chagall to shreds. ''I thought maybe I'd keep a little piece of it, but it smeared all over my hands,'' says Kenworthy. ''It was a bit of a mess.'' Just like true love.