Adults learned that Robin Williams was a comic genius (or an acquired taste), and kids learned the words na nu na nu and wiener. Spun off from an episode of ''Happy Days,'' Mork & Mindy stars Williams as Mork, a hyperactive alien from the feeling-free planet Ork, sent to Boulder, Colo., to observe emotive earthlings -- namely, Mindy (Pam Dawber), his roomie of infinite patience; her feisty grandmother (purveyor of the term wiener); and her uptight father (said wiener). Over the course of the obnoxiously laugh-tracked pilot and first 23 episodes, Williams offers plenty of warp-speed shtick (Mork takes everything literally because he's an alien!) and heartfelt moral reports to Orkan leader Orson that cover issues like democracy, ageism, and the power of hugs. Watch for David Letterman, who appears as a stylin' cad in ''Mork goes ERK.'' EXTRAS Don't bother looking for any.