The global PC market returned to growth mode in the third quarter, with shipments rising 2.3 percent compared with the same quarter last year, according to numbers released today by market research firm IDC.

The trend is good news for Microsoft, which relies heavily on sales of Windows preinstalled on computers. The Redmond company is launching the new Windows 7 operating system next week. The positive result for the market followed two quarters of declines in global PC shipments in the first half of the year. IDC said portable machines spurred the market.

“With the forthcoming launch of Windows 7 and expected commercial refresh beginning in 2010, the prospects for future PC market growth are very solid.” said Bob O’Donnell, IDC vice president of clients and displays, in a news release issued with the numbers.

It wasn't just Windows PCs seeing the benefit. Apple's U.S. market share rose to 9.4 percent for the third quarter, from 8.6 percent in the same quarter last year, according to the IDC numbers.

HP led the worldwide market, with global share of 20.2 percent for the quarter. Acer took the No. 2 worldwide slot, at 14 percent, compared with the 12.7 percent registered by Dell. HP also took the top slot in the U.S. market, with 25.5 percent, compared with 25 percent for Dell and 11 percent for Acer.

It's the second straight day of good news for the PC market, following a strong quarterly report from Intel yesterday. Microsoft reports its quarterly earnings Oct. 23, the morning after the Windows 7 release.

Update: Market research firm Gartner also shows the PC market growing again, albeit at a smaller 0.5 percent rate for the quarter. (Via Eric Savitz of Barron's Tech Trader Daily.)