Ursula Buffay, Phoebe's twin sister, is a waitress in the TV show Mad About You (1992). In this "crossover" episode between the two sitcoms, Fran (Leila Kenzle) and Jamie (Helen Hunt) visit Central Perk and mistake Phoebe for Ursula.
First appearance of Ursula, Phoebe's estranged twin sister, whose character was created to explain Lisa Kudrow's ongoing role as Ursula the waitress on the popular sitcom Mad About You (1992). As "Friends" aired on Thursday nights immediately after "Mad About You," the producers added Ursula to "Friends" to explain Kudrow appearing on back-to-back shows in different characters. She was first referenced in the second episode The One with the Sonogram at the End (1994), when Phoebe says her sister is a waitress, which was the first episode produced after the show was given the Thursday night timeslot.
The TV show playing when Monica has the manual and is trying to fix the SAP setting is an episode of The Patty Duke Show (1963), which was themed around Patty Duke playing identical cousins, Patty and Cathy Lane. This is similar to Lisa Kudrow playing both Phoebe and Ursula Buffay.
The building shown from the outside with the glass windows at 18:32 is the same building used in the opening credits of North by Northwest which started Cary Grant. Jennifer Grant, Cary Grant's only child, guest starred on this episode.
There was no original plan to reveal that Ursula, an established recurring character on "Mad About You", was Phoebe's sister. However, when NBC moved "Friends" from its initial 8:30PM EST timeslot to a 9:30PM one during February 1995 sweeps, the two-part storyline included a tie-in to "Mad About You" because it was the 8PM show to kick of Thursday nights. So it was decided to embrace the tie-in and make Ursula and Phoebe sisters; also, this would allow Ursula to be a recurring agent of chaos because Lisa Kudrow could play both roles.