Sales of Mac virtualization software from market leaders VMware and Parallels have shot up more than 50 percent this year, outpacing the 41 percent growth in Mac hardware sales experienced by Apple in the most recent quarter, according to market research firm NPD.

An article over at Computerworld notes that Parallels has sold over 1 million of its Parallels Desktop offering since 2006, while VMware, which only recently launched its Fusion product, says it sold 250,000 copies in the first five months.

Both solutions fetch $80, and therefore VMWare's come-from-behind effort has landed the company in a "neck and neck" race with Parallels in terms of shipments and unit sales, according to NPD software analyst Michael Redmond. Based on his firm's analytical data, he believes the Mac virtualization software market will grow into a $15 million - $20 million business this year.

"Clearly, the performance gains of [Macs] moving to Intel processors are encouraging more users to experiment with virtualization," Redmond said.

Earlier this week, the two Mac virtualization software makers intensified their head-to-head bout with product announcements and buying incentives.

VMWare announced version 2.0 of Fusion, a free download for version 1.x owners — $76 for new owners — that delivers experimental support for up to four CPUs per virtual machine, improved gaming graphics via DirectX 9.0's Shader Model, and virtualization support for Mac OS X Server.

Parallels, hard at work on version 4.0 of its Desktop client, countered with two promotional deals on its existing version. The first offers a free $25 iTunes gift card with the purchase of Parallels Desktop 3.0. A second offers the software to students for $49.99 through the end of the month.