You don’t hear much from Apple (AAPL) about the Mac’s worldwide market share, perhaps because it’s not as good a story as its U.S. share, which by most accounts grew from 4% to 5% over the past year (see Mac Sales Soar).

But Mac sales are growing almost as fast overseas — albeit from a lower base — according to the latest data from IDC. The chart below shows Mac global market share growing from 2.1% last year to 2.6% in the quarter that just ended, a shade under 20%.

PiperJaffray analyst Gene Munster, who had expected the Mac to lose market share in Q1 of calendar 2007 (which Apple refers to as Q2), was pleasantly surprised that it had inched up a bit from the Christmas quarter, from 2.5% to 2.6%. And he believes it’s uphill from here for the rest of the year. AppleInsider summarizes the letter Munster sent to subscribers yesterday:

First and foremost, he said, the company’s dominance in the portable sector will only help to amplify Mac appeal as the industry continues its trends away from clunky desktop systems and towards notebooks. He also noted that iPod and iTunes users on the Windows side are increasingly switching to Macs because they offer superior media management.

“And with iPhone and Apple TV, Apple has carried its lead in music into two new product categories,” Munster told clients. “These products will further expand its footprint in a market with growing demand for simple solutions for digital content management. So far Dell and HP have failed to deliver PCs that rival the Mac’s superior media experience.”