Rising consumer interest in media tablets like Apple’s iPad is beginning to take a toll on the global computer market, with shipments of desktops and notebooks in the first quarter of 2011 declining compared to the same period in 2010, according to new IHS iSuppli (http://www.isuppli.com) research.

Worldwide computer shipments amounted to 81.3 million units in the first quarter of 2011, down 0.3% from 81.6 million during the first quarter of 2010, says the research group. Three out of the world’s top five computer makers suffered year-over-year declines in shipments during the quarter (but, interestingly, not Apple).

No. 3-ranked Acer, which sells a high proportion of netbook-type computers that face a direct competitive threat from media tablets, bore the brunt of the downturn, with its first-quarter shipments plunging by 20.4% to 9.2 million units, down from 11.6 million during the same period in 2010.

“The increasing momentum of the media tablet market, led by the iPad, is creating a difficult environment for the PC industry,” sys Matthew Wilkins, principal analyst for compute platforms research at IHS. “All the attention surrounding tablets contributed to weak consumer demand for PCs in the first quarter.”

And although corporate computer demand was strong, it wasn’t enough to offset the decline in consumer sales.

“IHS believes that the jury is still out on exactly how much tablets are cannibalizing PC sales,” Wilkins says. “However, the rising number of tablet models on the market, along with certain high-profile product launches during the first quarter, caused confusion among consumers as to exactly how to view the tablet platform relative to the PC platform. This contributed to the PC sales decline in the first quarter.”

The first-quarter decline came as somewhat of a surprise, given that the fourth quarter represented the best period ever for global computer sales as computer shipments hit a new quarterly record, blowing past the previous high of 88.9 million units set in the fourth quarter of 2009. Corporate demand had been driving growth of the market.

Despite the first-quarter weakness, computer sales growth should return later in the year. The current IHS iSuppli forecast predicts the global computer market in 2011 will expand by 8% to 373 million units, up from 345 million in 2010. This compares to 14% growth in 2010.

Hewlett-Packard Co. continued its reign as the No.1 computer vendor in the first quarter of 2011, with a market share of 18.9%. The company suffered a 2.1% decline in sales compared to the same time a year ago because of the difficult conditions in the consumer market.

Dell continued to hold on the No. 2 position over third-ranked Acer in the first quarter, with a market share of 12.9%. Rounding out the top five were Lenovo and Toshiba, which coincidentally were the only top five computer original equipment manufacturers (OEM) to achieve growth in their total shipments over those from the first quarter of 2010. Fourth-ranked Lenovo and fifth-ranked Toshiba achieved market share positions of 10% and 5.8%, respectively.