HP has expanded its lead over Dell in the overall PC market during the third quarter, while Acer snatched the number two spot from Dell in notebooks, according to market researcher iSuppli.

HP's market share rose to 19.2 percent as it widened its lead over second place Dell, which held a 14.6 percent share, iSuppli reported in preliminary figures. It's a remarkable difference from the same time last year, when HP first captured the top spot from Dell with a 16.5 percent market share, versus 16.3 percent.

Dell has suffered from a host of troubles over the past two years, including financial restatements and leadership changes. But its main problem has been a failure to grow as fast as rivals despite strong global PC market growth. The company's quarterly earnings conference on Thursday highlighted this issue. Despite strong revenue growth, rising costs cut into profits and the company warned that future earnings could be hurt by cautious PC buying among financial customers.

Rivals have taken advantage of its troubles.

HP has surged under fresh leadership from CEO Mark Hurd. The company's third quarter PC shipments grew 32.7 percent compared to last year to 13.1 million units, iSuppli said. Dell's increased just 1.5 percent to 9.9 million.

Acer added to Dell's woes in the quarter, snatching away the second place global ranking in laptop PCs on strong shipment growth. The Taiwanese company gauged the strongest growth among all top PC vendors in the third quarter, up 68.8 percent year-on-year, mainly due to strong notebook PC sales.

The market for notebook PCs is growing far faster than desktops, and offers far better profit margins for companies. Laptop shipments grew 33.5 percent year-over-year in the third quarter, while desktop PC shipments grew just 3.4 percent, iSuppli said.

Acer captured a 7.9 percent share of the global PC market in the third quarter, but the results did not include Gateway, which Acer recently acquired. Gateway figures will be included in fourth-quarter figures, iSuppli said. The addition of the U.S. company's sales will narrow the gap between Acer and Dell in global rankings.

Notebook shipments should continue to boost Acer. Goldman Sachs has revised its target for global laptop shipments up to 11 percent quarter-on-quarter growth in the fourth quarter, compared to a previous forecast of 9 percent. The investment banking firm also sees the potential for the best laptop shipment performance in six-years in the first quarter of next year.

iSuppli predicts worldwide PC shipments will grow 12 percent year-over-year in 2007.

The global PC market grew 13.8 percent year-on-year in the third quarter as companies shipped 68.1 million PCs, iSuppli said. Chinese PC vendor Lenovo retained its third place global ranking in the PC market in the third quarter with an 8.1 percent share, while Acer took fourth and Toshiba placed fifth at 4.3 percent.