Although they disagree, as usual, about the details, the message from Gartner and IDC‘s quarterly PC market share reports Wednesday was the same: Apple is going gangbusters, the rest not so much.

IDC’s Bob O’Donnell puts it most succinctly:

“Apple’s influence on the PC market continues to grow, particularly in the U.S., as the company’s iPad has had some negative impact on the mininotebook market. But, the halo effect of the device also helped propel Mac sales and moved the company into the number three position in the U.S. market.”

Contrast that with what IDC has to say about U.S. PC sales overall:

“Weak back-to-school sales and consumer fatigue characterized the market. The region grew 3.8% compared to a year ago, 7% below forecast.”

IDC has Apple third-quarter Mac shipments in the U.S. growing 24.1% year over year as its market share hit double digits (10.6%) for the first time since the early 1990s. Apple (AAPL) is now the U.S.’s No. 3 computer maker in IDC’s ranking, after Hewlett-Packard (HPQ) and Dell (DELL).

Apple is No. 4 in Gartner’s list with a 10.4% market share, just behind Acer at 10.5%. Neither company counts iPads as PCs, although they do count netbooks.

Below: IDC and Gartner’s Q3 spreadsheets for the U.S. market. Apple doesn’t appear in either’s worldwide market share report because it is still not one of the top five or six PC makers globally.

IDC:

Gartner:

You can read IDC and Gartner’s press releases here and here, respectively.

[Follow Philip Elmer-DeWitt on Twitter @philiped]