Most networks try to hide from their slimy pasts. Nickelodeon joyously wallows in the green goo.

The "kids-first" cable network turns back the clock Saturday with the start of a two-day programming block commemorating the channel's 20th birthday.

The celebration showcases some of the cable network's most memorable and innovative shows from the past two decades as well as a look back at some young performers who turned into stars.

A 1993 episode of "You Can't Do That on Television" (Saturday at 6 a.m.) shows Alanis Morissette, then a series regular, getting slimed. The singer is among more than 36,000 kids who have gotten a face-full of the signature slop. Celebrity slimings (featured in clips throughout the weekend) include Steven Spielberg, James Earl Jones, Rosie O'Donnell, Coolio, Sean "Puffy" Combs, Carrot Top, Joe Namath and the "Home Improvement" kids, Jonathan Taylor Thomas, Zachery Ty Bryan and Taran Noah Smith.

Future "Dawson's Creek" hunk James Van Der Beek got sloppy in another way: In an episode of "Clarissa Explains It All" (June 27 at 1 p.m.), he gave star Melissa Joan Hart her first on-screen kiss.

Other celebrity sightings include Neve Campbell on "Are You Afraid of the Dark," future Backstreet Boy A.J. McLean in the Nick at Nite series "Hi Honey, I'm Home," and -- perhaps foreshadowing his ability to pick scripts -- Will Fredell, later featured in "Zoe, Duncan, Jack and Jane," in an episode of "Don't Just Sit There."

Other highlights:

First episodes of landmark animation series "Doug" (Saturday at 8 a.m.), "Rugrats" (Saturday at 8:30 a.m.) and "Ren & Stimpy" (Saturday at 9 a.m.). There also are firsts of toons "AAAHH!!! Real Monsters," "The Wild Thornberrys," "Hey Arnold!" "Catdog" "Angry Beavers," "Rocko's Modern Life" and "Kablam!" and live-action series "Roundhouse," "The Journey of Allen Strange" and "The Secret World of Alex Mack."

Another look at game shows "Double Dare," "Figure It Out" and "GUTS."

CAPTION: "Rugrats' " Tommy Pickles is among the celebrants of the cable channel's 20th birthday.