Paula Zahn is leaving CBS News for the world of cable, where she will anchor a one-hour nightly newscast on Fox News Channel starting March 1. Zahn, 42, has most recently anchored the "CBS Evening News" Saturday edition and filled in for Dan Rather when he was absent during the week. She was co-host of "CBS This Morning" for six years. "The Fox Report," the network's signature evening newscast at 7 p.m., was anchored by Catherine Crier and Jon Scott until they left to host a newsmagazine for the Fox network. Now Zahn will take over. (According to the Associated Press, Fox News Channel has recently been on a roll, frequently beating its closest rival, MSNBC, in prime-time ratings.) Zahn also will anchor another hour of Fox News Channel programming on weekdays.