(This new column will report on primetime ratings every Tuesday.)

More than 23 million tuned in to see Kristy Lee Cook’s ouster on last week’s American Idol results show, which helped Fox win the week ending April 20 with an average 8.8 million viewers. Meanwhile, Desperate Housewives ranked as the most-watched drama in primetime and Two And A Half Men continued its reign as the most watched sitcom on TV (sorry, The Office, No. 21, and 30 Rock, No. 44).

The 10 most-watched new shows from last week: Idol Tuesday (23.6 million), Idol Wednesday (23.3), Dancing with the Stars (17.1), Housewives (15.7), Dancing results (15.4), NCIS (15.1), Men (13.9), CSI: NY (13.4), Law & Order: SVU (13.2), and Criminal Minds (12.9). Biggest Loser 5, which ended its run last week, averaged 11.3 million viewers, while the controversial Democratic Presidential Debate (swell questions, Charlie!) attracted 10.6 million.

Who’s winning the 2007-08 season so far? Fox (no surprise) is averaging a respectable 11.3 million, followed by CBS (10.5), ABC (9.1), NBC (8.3) and CW (2.6). Fox is also leading in the all-important 18-49 demographic (4.3 rating/11 share), followed by ABC (3.0/8), CBS (3.0/8) NBC (2.9/8) and CW(1.0/3). Each rating point represents 1.31 million viewers.

And finally, of the Big Four networks, Fox is currently attracting the youngest viewers (average age of 43.9), followed by NBC (48.1), ABC (49.1) and CBS (51.9).