AND WAIT, THERE'S MORE: Odd Couple alert! Joni Mitchell and Billy Idol, singing together? Could it really be? Well--almost. Mitchell has finished up a new album, titled "Chalk Marks in a Rainstorm," which is due out at the end of February on Geffen Records. And believe it or not, Idol helps out with the vocal chores on "Dancing Clown," though we hear it's not really a full-scale duet. Mitchell has plenty of other superstar assistance, including Willie (Have Duet, Will Travel) Nelson, who teams up with Mitchell on "Cool Water," Peter Gabriel (who croons on "My Secret Place"), Don Henley (vocals on "Snakes and Ladders"), Wendy & Lisa (who sing on "The Tea Leaf Prophecy"), Thomas Dolby, Ben Orr, saxophonist Wayne Shorter and veteran Western film star, Iron Eyes Cody, who performs an Indian chant on a song called "Lakota." . . . J. J. Jackson is the new music director at KMPC-FM (The New FM 102), where he'll also hit the air Monday as the station's new afternoon-drive deejay. . . . Rosie Flores will perform live (with her band) on a special edition of Rene Engel's "Citybilly" show Tuesday at about 9 p.m. on KCRW-FM (89.9). . . . And the Bonedaddys, one of the local club circuit's steamiest dance bands, have signed with Chameleon Records, which will release the group's debut album at the end of January. Titled "A-Koo-De-A," it features such songs as "She's the Lion," "Zouk Attack" and "Dumpster Girl"--and will feature the band's new lead singer, Kevin Williams, who recently replaced the departed King Cotton.