In Part 1 of the two-part season finale of 7th Heaven (8 p.m., WB), Mary falls in with bad news Robbie again, and Matt realizes he's still in love with Heather. Catfight alert: Nelle steals Ally's clients, prompting legal action by the firm, on Ally McBeal (9 p.m., Fox). On Everybody Loves Raymond (9 p.m., CBS), Robert returns to work after his bull-goring accident, but freezes up during a confrontation. On the season finale of Roswell (9 p.m., WB), Max defies his alien destiny to be with Liz. For some reason, Backstreet Boy Howie Dorough has a cameo. On 48 Hours (10 p.m., CBS), journalism students attempt to solve a 13-year-old murder case.
Whitney Houston makes a rare noncanceled appearance on 25 Years of Number One Hits: Arista Records' Anniversary Celebration (8 p.m., NBC). Also performing: Santana, Aretha Franklin, Barry Manilow, Sarah McLachlan and Patti Smith. President Harrison Ford kicks terrorist butt in the network premiere of Air Force One (8 p.m., ABC). In the four-part series Secrets of the Dead (check local times, PBS), scientists revisit the causes of some of history's cataclysmic events, beginning with a probe into the catastrophe that might have led to the Dark Ages.
Avalanche at Stars, Western Conference Finals, Game 2 (7 p.m., ESPN)
Rosie O'Donnell (syndicated) Macy Gray
David Letterman (CBS) Gillian Anderson
Jay Leno (NBC) Richard Harris, Sea World animals
Politically Incorrect (ABC) Steve Harvey, Joey McIntyre
Conan O'Brien (NBC) Ashley Judd, Shelby Lynne (rerun)