Hunkered down in a London studio as they start to work on — albeit tentatively — a new album, U2 has recorded a special duet with Green Day that both bands will debut live in New Orleans on the Sept. 18th edition of Monday Night Football, when the Superdome reopens for the first time since Hurricane Katrina. The song they've chosen for their first—ever collaboration is "The Saints Are Coming" by The Skids. "It really is a slice of pure post—punk rock," U2 guitarist The Edge says via phone from the band's studio during a break in recording. "It's pure 1978, a song that was a big inspiration to us at the time and couldn't be more in the sweet spot of what Green Day are about. It perfectly intersects our mutual interests in musical terms. It's been great fun to play that tune with Green Day, who are great players and have the right stuff."

Both bands hope to release "The Saints Are Coming" as a single, with proceeds going to Music Rising, the fund started by The Edge and others to provide relief to New Orleans' musicians. So far Music Rising has provided more than 2,000 people with instruments and aid, and has designs on helping churches and schools replace thousands more lost and damaged instruments.

If the song seems an esoteric choice for two multi-platinum acts, it is. The Skids had a brief but glorious run in the late 70s, but in the U.S. singer Stuart Adamson, who died in 2001, is better known as the leader of Big Country, the band he started after The Skids broke up. But while not many people know "The Saints Are Coming", the song fits the occasion. (Sample lyric: A drowning sorrow floods the deepest grief/ How long now, until a weather change condemns belief.) "It's a bit of mournful sentiment," says the Edge, "but we play it pretty fast, definitely under three minutes. This is playing with intent. We want to get to the point." And who plays lead guitar? "That's the great thing about punk rock," laughs the Edge. "It's anti the concept of lead guitar."

Meanwhile The Edge adds that U2 is working with producer Rick Rubin on their new album. "We are really enjoying the chemistry," he says. "It's too early to say where it's going to lead—we're nowhere near any kind of timetable or anything?but we're having a good time." Rubin has produced albums by everyone from Run DMC, Beastie Boys, and Red Hot Chili Peppers, to Dixie Chicks and Johnny Cash, but this is his first time working with U2. "I have a feeling that because of Rick's presence and some other things as well that it's going to sound very different," continues the Edge. "When people spend time with it, they'll pick up on a different spirit, and I think it is a departure. We don't want to spend a whole lot of time on this album, so hopefully we'll get on a roll and get it out there. But really, it's early days."