Dell's retail strategy to distribute PCs is starting to show results, helping extend its lead over Hewlett-Packard (HP) as the largest U.S. PC vendor in the fourth quarter of 2007, according to figures from analyst firms Gartner and IDC.

However, HP remained the world's largest PC dealer, topping Dell, Acer and Lenovo, according to figures from both firms.

Dell shipped 5.5 million units in the U.S., a 15.2 percent year-over-year increase and a 29.6 percent market share, according to IDC. HP, in second place, shipped 4.5 million units, a 9.8 percent year-over-year increase and a 24.3 percent market share. Acer, in third place, showed tremendous growth in the U.S., with shipments increasing 294.2 percent to 1.5 million units. Apple's shipments grew 30.9 percent to 1.06 million, a 5.7 percent market share. Toshiba was in fifth place, IDC said.

Gartner reported that Dell shipped 5.35 million units, with a 31.4 percent market share during the fourth quarter, compared to the 29.3 percent market share it had last year. HP shipped 4.4 million units, with market share growing to 26.1 percent from 25.5 percent last year. Acer and Apple were in third and fourth places, respectively.

Dell's switch from a direct sales model to selling PCs through retailers like Best Buy and Wal-Mart is paying off and has helped the company improve shipments, said David Daoud, an analyst with IDC. "They're coming out of nowhere to everywhere," Daoud said.

However, Dell is trying to catch up internationally with HP, which is investing more in distribution channels and understands business behavior in emerging markets better, Daoud said.

According to IDC, HP shipped 14.7 million units worldwide, a 23.3 percent year-over-year growth and a 19 percent market share. Dell was in second place, shipping 11.3 million units with a 14.6 global market share, a 17.1 percent rise from the previous year. Acer saw a sharp rise, with shipments growing 60.3 percent year-over-year to 7.4 million. Lenovo came in fourth, shipping 5.8 million units, a 22.3 percent year-over-year increase. Toshiba was in fifth place.

The acquisitions of Packard Bell and Gateway last year helped boost Acer's shipment volumes globally, though the companies have not yet fully contributed. "Given the acquisitions are relatively recent, it will takes years or more to see tangible results," Daoud said.

Acer's acquisitions have taken a bite out of Lenovo, which saw slower growth in the global market and is struggling to retain its core audience of business users, Daoud said. With the launch of the IdeaPad notebook, Lenovo is trying to expand to the mass consumer market, which has alienated its traditional business users. Lenovo needs to reassert its commitment to business customers, Daoud said.