NBC is promoting its prime-time lineup tonight as "must-see TV" of the highest order -- and in many respects, it's right. Bebe Neuwirth returns as Lilith on a hilarious episode of "Frasier," "L. A. Law" has a couple of tense scenes featuring some talented players, and "Mad About You" presents a virtual-reality show that's virtually perfect. Also tonight, but on CBS: Robert Culp and Bill Cosby reunite in the made-for-TV movie "I Spy Returns."
* "Mad About You" (8-8:30 p.m., WMAR, Channel 2) -- VCR Alert: The premise of this show is so clever, and its treats so delightful, it indeed IS must-see television. The plot has Jamie (Helen Hunt) and Paul (Paul Reiser) arguing about whether to invest in a new-generation virtual-reality machine -- and individually trying it out, tapping into their own fantasies. NBC has promoted this episode so much that the appearance of Christie Brinkley is no surprise -- but the playful high level of her performance is, and the best news of all is that this attention-getting "Mad About You" is perfectly true to the intimate dynamics of Paul and Jamie. NBC.
* "I Spy Returns" (8-10 p.m., WBAL, Channel 11) -- This series doesn't devote quite enough time to the charming byplay of Mr. Culp and Mr. Cosby, but it's nice to hear the "I Spy" gunshots and theme song again -- and in Salli Richardson, as the feisty daughter of Mr. Cosby's Scott, this pleasant reunion has showcased a promising young talent. CBS.
* "The Simpsons" (8-8:30 p.m., WBFF, Channel 29) -- Conan O'Brien is shown in animated form on tonight's "The Simpsons," the series on which he used to serve as a writer-producer. Interestingly, this won't be Mr. O'Brien's cartoon debut: He was seen entering a restaurant on last week's "The Critic." Fox.
* "Wings" (8:30-9 p.m., WMAR, Channel 2) -- Gilbert Gottfried guest stars on tonight's "Wings," along with William Hickey. NBC.
* "Seinfeld" (9-9:30 p.m., WMAR, Channel 2) -- On "Seinfeld," in an episode unavailable for screening, the "puffy shirt" is joined, in this show's ever-growing lexicon, by George's "puffy coat." Jerry Seinfeld, Jason Alexander star. NBC.
* "Frasier" (9:30-10 p.m., -- Ms. Neuwirth's Lilith shows up in Seattle, and she's far more than just sleepless. The way in which she interacts with the regular cast members of "Frasier" is an absolute joy to watch, and it makes this "Frasier" a keeper: VCR Alert. Kelsey Grammer stars. NBC.
* "L. A. Law" (10-11 p.m., WMAR, Channel 2) -- Joan Spencer and Joanna Cassidy get some good scenes here, as does A Martinez, but the showstopper is the smoldering scene between Corbin Bernsen's Arnie Becker and Alexandra Powers' Jane Halliday. NBC.