Two doses of good news for fans of Nickelodeon's "Roundhouse": The spirit of that funny sketch comedy continues on the cable station with a new Saturday night parody series, "All That," and "Roundhouse" regular David Sidoni is hosting a Friday night lifestyle magazine show, "Bing, The Sound of Something New." Though billed as "not quite live or ready for prime time," "All That" features a seven-member cast (ages 12 to 18) that consistently produces laughs with on-target schtick reminiscent of old "Saturday Night Live" episodes. Recurring characters include funny Ross Perot and Bill Cosby knockoffs, a goofball counter dude at a fast-food restaurant, the well-meaning Mavis and Clavis, a lactose-intolerant superhero, and chocaholic chefs Randy and Mandy -- who get laughs by playing to the unwritten Nickelodeon credo, "Make a mess." The half-hour show was created by Brian Robbins, who starred in "Head of the Class" with "All That" producer Dan Schneider. Malcolm-Jamal Warner will direct three of the 13 episodes (airing Saturdays at 8:30 p.m. and repeating Sundays at 1 p.m.). Each show features a red-hot musical guest, such as Super Dude, Da Brat, TLC, Immature, Coolio, Aaliyah, Usher Raymond, Brandy, Soul IV Real and Craig Mack. (Kids will know the names, even if their parents don't.) "Bing" (airing Fridays at 7:30, repeating Saturdays at noon) also uses a tried-but-true formula adapted to the current scene. The half-hour show promises to deliver "what's new and what's next" in music, trends and movies, emphasizing the point with a fast-paced format and hand-held camera work. Everyman-host Sidoni thus far has garnered interviews with Sinbad (while doing the actor's yard work), singers All 4 One and hockey star Wayne Gretzky. Segments have focused on CD-ROM technology that allows kids to play along with rock bands, snowboarding and shaking movie theaters. "Bing" also uses kid-on-the-street interviews and computer on-line polls to allow viewers to contribute information about themselves. CAPTION: David Sidoni (getting pointers from guest Sinbad) hosts Nickelodeon's herky-jerky news magazine, "Bing, The Sound of Something New."