The message boards are rocking. Does Kyle Gass, half of cheerfully demented music duo Tenacious D, make a cameo in pal Jack Black's ''School of Rock,'' like he did in ''Shallow Hal,'' ''Saving Silverman,'' and ''Bongwater''? ''No, he did not appear in the film, and I know it's going to cause a stir,'' laughs Black. ''But there wasn't any really good part for him. I guess he could have been one of the teachers with, like, one line, but that wouldn't have been cool.'' Better to save the juice for their quest comedy ''Tenacious D in 'The Pick of Destiny,''' which the duo plans to start shooting in January (Liam Lynch will direct). In the meantime, Gass is down with Black's solo on-screen antics: ''Obviously they took a lot from Tenacious D, and didn't give me credit, but, you know...'' Ooh, tension in the band. (Additional reporting by Adam B. Vary)

