Sweeney's work has taken him across a variety of musical genres. Starting in 2000 he turned up on Cat Power's "The Covers Record", playing guitar on "Salty Dog", and a couple of Bonnie "Prince" Billy singles (percussion on "A Whorehouse is Any House" and guitar and vocals on "Little Boy Blue"). In 2001 he started playing and writing with Billy Corgan and Jimmy Chamberlin in what was to become Zwan. He collaborated with Billy Corgan on the soundtrack to the movie "Spun", singing the movie's opening song, a cover of Iron Maiden"s "Number of the Beast". He was also featured as a guitarist and backing vocalist on Bonnie "Prince" Billy's "Ease Down The Road" album. He lent a helping hand to Dave Grohl in assembling the all-star heavy metal album Probot, tracking down the legendary singers and providing some guitar work (the Probot album was not released until 2004, on Southern Lord records). Sweeney recorded and toured with Zwan from late 2001-2003. He is credited as providing guitar, vocal, and some songwriting on Zwan's album "Mary Star of the Sea".