Write what you know. That's the usual maxim for first-time novelists. And so it was for Entertainment Weekly senior writer Rebecca Ascher-Walsh and former Fortune Senior Editor Erik Torkells. Teaming up under the pseudonym C.J. Tosh, the duo penned ''Bite'' (Downtown, $22), a high-gloss novel following the professional and personal travails of Samantha, a posh writer for the showbiz weekly ''Star Face,'' and her gay buddy Tom, an editor at the finance mag ''Profit.'' But this is no roman a clef. ''Sam is thinner and cuter and single,'' says Ascher-Walsh. ''But her office is just as messy.'' And unlike her heroine, she's never been fired for rumors that she, ahem, got too intimate with Russell Crowe.