''It's an OutKast album in visual form,'' says Antwan Patton (a.k.a. Big Boi) of Idlewild, a 1930s-set musical in which he and cohort André (3000) Benjamin star as jazzmen. Written and directed by music-video vet Bryan Barber, Idlewild (due 2006) also features Terrence Howard as a gangster muscling in on Big Boi's juke joint. How did OutKast enjoy acting while writing and performing the tunes? Benjamin sums it up: ''All I can say is: madness.''