Beneath the Guggenheim on upper Fifth Avenue, more than 300 patrons have packed the Peter B. Lewis Theater--filled the seats, lined the walls, clogged the aisles--for the first-ever showing of Informal, a 13-minute dance performance choreographed by Pam Tanowitz with original music by composer Dan Siegler, Tanowitz' husband.

For the 31-year-old choreographer, this is more than just a world premiere: It's an uptown premiere.  "This is a whole new audience," Tanowitz says excitedly, "new exposure to people who wouldn't necessarily come downtown." Like way downtown, to Avenue C, where Tanowitz founded the Open 24 Hours Dance Company with a couple of friends in 1992.

Her choreography, honed at Ohio State and Sarah Lawrence, is a blend of ballet and modern (this isn't mixed-media dance theater or experimental performance art.)  In many ways, the Guggenheim show in March was simply the first uptown performance of dance that is already very "uptown" in sensibility.

The same can be said for Siegler's music, written in this case for piano, cello, and violin.  Informal is the couple's fifth collaboration in five years.

"A lot of choreographers would love a live-in composer, let me tell you," Tanowitz says.  "I mean, hey, free music."

Seigler also writes songs for films and plays, but he says writing music for dance gives him the most independence to express himself.

"We found a hopefully interesting middle ground," Siegler says.

The couple says collaborating fits naturally into their lives.  Tanowitz and Siegler also co-own a restaurant, the L Cafe in Williamsburg. But so far their favorite collaboration is new baby Gemma, born December 31st.

Meanwhile, Tanowitz has been invited to perform this summer at the American Dance Festival at Duke University, one of the most prestigious dance events in the country.  "All I do is keep making dances and keep trying to show them," she says with a shrug.