Is she ready for her acting career to Blossom again? Not so much, but Mayim Bialik did take a brief break from her Ph.D. studies in neuroscience to make her first prime-time network appearance since, well, Blossom went off the air in 1995. She'll guest-star on the May 5 episode of 7th Heaven as a grifter who's counseled by Chandler (Jeremy London). ''It was nice to play an adult role, not an age with a 'teen' after it,'' notes Bialik, who was sent the script on a whim by Heaven creator (and former Blossom scribe) Brenda Hampton.... Whitney Houston will give Boston Public the greatest love of all -- a guest appearance on the season finale, airing May 12. In the episode, the diva accepts a student's invitation to attend the prom and winds up performing a song from her latest album.... CBS has discovered the joy of supersizing and will expand two of its mainstays for the last week of sweeps: On May 19, the network will tack an extra 15 minutes each onto the season finales of Everybody Loves Raymond and CSI: Miami.