For work, Joss Whedon writes scripts for Buffy the Vampire Slayer. For play, he tried something different: He wrote a Buffy musical.

"I love musicals more than any old thing, but I just never thought I'd have the time," says Whedon, the Buffy creator and executive producer who took advantage of his first vacation in years to compose words and music for tonight's episode, "Once More, With Feeling" (8 ET/PT).

Whedon, who describes his musical training as "a few lessons on piano," says he writes songs in his spare time and thought a musical Buffy was tantalizing. The cast liked the idea, though some were apprehensive because of varying degrees of musical experience.

"I sort of knew what I was dealing with, who was most comfortable singing, who was most comfortable dancing," he says.

He knew, for example, the kind of songs James Marsters (Spike) liked to sing and knew of Michelle Trachtenberg's (Dawn) preference for dancing.

"I was surprised everybody did so well," Whedon says, offering proof: "No one had to be dubbed."

Guest Hinton Battle added some dazzling malevolence as the villain, Sweet, who casts a singing-and-dancing spell on Buffy (Sarah Michelle Gellar) and the gang.

Whedon was pleased with the support from his new network UPN, which agreed not only to the musical but also to an eight-minute extension of Buffy's hour.

"I really tried hard to get it down to the normal time, (but) it just wasn't as good at the shorter length," he says.

After a tumultuous shift from WB to UPN this year, Whedon says he is happy. After a few years at WB, the network was "sort of used to us," while UPN treats the show as a new star attraction.

"They're so supportive. They've done so much publicity," he says.

For the musical, UPN held a premiere and put up billboards with musical notes in Buffy's eyes.

"I thought it was one of the best episodes of television I ever saw in my life," says UPN president Dean Valentine, who says the show has picked up more male viewers since its move from WB. "Men like shows with girls who kick a--."

Surprisingly, Whedon says composing the musical's words was tougher than its melodies.

"It's much harder," he says. "You have to rhyme them, too."