Lehman shares [LEH 23.75 --- UNCH ] plunged pre-market amid news that CFO Erin Callan and operating chief Joseph Gregory were ousted from the struggling brokerage firm. Both had publicly smacked away rumors that the firm was financially unstable as the stock came under attack from short sellers; this week news broke that Lehman would take a bigger loss than expected and that it was raising $6 billion in fresh capital. There were murmurs that it might even need to raise more.