If last week was about selling energy and materials to buy tech, this week was the mirror image. In a seemingly illogical turn of events, the tech sector stumbled despite strong earnings from several bellwether companies, while energy was the best-performing sector amid plunging oil prices. The sum of the parts was a lot of volatility, investors getting the usual jitters about earnings, and blue-chip indices and bond yields that were flat on the week. The Nasdaq Composite, conversely, did not emerge unscathed. Apple ( AAPL) led the Nasdaq to a new six-year high last week, and just as swiftly led the index's 2.1% plunge in this round. Enthusiasm for the iPhone faded as investors gathered anxiety about CEO Steve Jobs and the government's investigation into options backdating. Shares of Apple fell 7.6% on the week. Investors also debated the strength of Apple's midweek earnings report. The company beat estimates but provided its usual dose of conservative guidance. The same was true for Intel ( INTC), which also beat earnings estimates earlier this week, yet warned that its profit margins would be stunted throughout 2007 due to its price war with competitor Advanced Micro Devices ( AMD). Shares of Intel and AMD fell 5% and 12.1%, respectively. IBM couldn't catch a break, despite an impressive quarter as well. Big Blue's shares slid 2.5% on the week, and Cisco's ( CSCO) fell 6.7%.