BACK IN 1969, the buzzword was that anyone could do anything. Andy Warhol said everyone could be famous for 15 minutes. People who couldn't hold a paintbrush displayed their own spatter paintings on their walls. And Twyla Tharp declared that Joe Ordinary was capable of performing a piece of her choreography for 11 seconds. Eleven seconds precisely. She'd had this beatific dream, lying blissed out on a grassy hillside (it was the 1960s, remember), and conceived the notion of a dancework composed of 100 phrases of movement. They could be performed in sequence, to make a long piece, or all at the same time, to make a very short one: an eruption of dense activity, 11 seconds from start to finish. And the dancers could learn the wherewithal in one afternoon

It was a fine idea to launch Twyla Tharp's two-week season at the Barbican with a recreation of The One Hundreds, and for the 100 punters who signed up for the workshop I can believe it was a wholly enlightening experience. For the audience, however, the performance on Monday smacked more of an evening at Butlins. Tharp is a most eloquent demonstrator of her craft. But give her a microphone and this gift of the gab begins to swamp the work. What was billed as a lecture-demo was dominated by silly sideshows: a contest for the most authentic 1969 get-up, a contest between two of her company dancers (who performed the 100 phrases end to end with impeccable synchronisation); judged by how hard the audience clapped (for heaven's sake!). The innovative nature of the movement itself came a poor second to this self- congratulatory tosh. And these ideas, in their time, had been revolutionary.

It all looks so easy. You see a phrase based on someone hitting a golf ball, another on a pregnant woman's walk, an imitation of an aeroplane, even one of Elvis Presley's leg-shakes. A major Tharp hallmark is her ability to pluck out movements familiar in everyday life and weave them into the flowing fabric of dance. Performed in sequence by trained dancers the effect is neat, pointed and amusing. Performed in one go by 100 people with feet of clay the effect is, well, shall we say, colourful. And brief. On Monday there was a satisfying irony in seeing 100 bodies scrabbling on to the stage to take up their positions and - 11 frenzied seconds later - all scrabbling off again. They enjoyed themselves, at least.

A more sophisticated account of the choreographer's creed came next day in a revival of her 1970 work, The Fugue. On a floor miked for sound, three men in hard brogues create a tense, unaccompanied counterpoint from a basic 20-count phrase, developing ever more tortured rhythms by means of stamping, clicking and sashaying feet - almost like flamenco - before converging again in a kind of resigned unison. It's hard to imagine how stark and exciting this would have seemed 30 years ago. Significantly, it still came across as the most "modern" work on the bill.

Roy's Joys (1997) is unashamedly retro. Nine dancers, nattily dressed in pistachio and mauve chinos, flirt and hula-hoop their way through the delicious bebop songs of Roy Eldridge, sometimes bouncing full-length on the floor like jelly beans, or soaring in balletic flick-jumps that blend seamlessly into the loose-limbed jazz-dance feel. It's this ease of assimilation that puts the Twyla stamp on a work. You'd be hard pressed to say how her fabulous dancers were trained: ballet, jazz or Cunningham- modern? Tharp bundles all these influences together in one heart-gladdening package that has become entirely hers.

Yet Yemaya, the newest work, is an even more surprising turn-up for the book of Tharp. It's a mini-drama, no less. A Cuban musical medley drives the opening cocktail scene, spiked with jealous tiffs between foxtrotting couples. Then tough guy Andrew Robinson gets seduced by a South African voodoo fertility goddess. Cue endless hot-blooded pounding of tribal drums. It's all very Club Tropicana and, coming from Twyla Tharp, all very odd. But then, after 30 years at the leading edge of cool, perhaps she's entitled to remind us that we ain't seen nothing yet.

A very different strand of all-American dance was presented at the South Bank in the form the New York Ballet Stars. Since this country never gets to see the full New York City Ballet (too expensive to bring over) this brief masterclass in the Balanchine style was most instructive. It's so different: faster, leggier, and with its own brand of ballet chic. The women are in neat little tunics and diamond ear-studs; the men beam fresh-faced Broadway pizzazz, while adhering to the strictest code of classical bearing.

Their mixed bill showed the ways current New York ballet-makers have found to deploy the distinctive aesthetic developed by Balanchine, the company's founder. Ironically, a new work by the British Christopher Wheeldon looked far more conservative than Balanchine's own Apollo, made in 1928. But Ulysses Dove's Red Angels, set to some very funky electric violin, played live, and was hotter even than the title led us to expect. Ankles whistled past cars in rapid high-kick extensions, rib cages undulated like cobras and bodies spun on the spot like bore-drills. Technical bravura doesn't come much braver. In a more contemplative vein of invention, Christopher d'Amboise's Circle of Fifths made ingenious play with movement triggered by fingertip contact - recalling God's Renaissance connection with Adam. There, too, were the clever swallow formations in the corps that you see in the big Balanchine works, but beautifully reworked.

Tharp!: Barbican, EC2 (0171 638 8891), to Sat. New York Ballet Stars: QEH, SE1 (0171 960 4242), ends tonight.