Apple has turned its sights on the vulnerable prey of Microsoft’s Windows Vista by previewing “Leopard”, the next version of Mac OS X.

At its Worldwide Developer Conference in San Francisco this week, Apple chief executive Steve Jobs paved the way for a release of the operating system in spring next year. Vista is scheduled for a consumer release in January but many observers expect even that delayed date to slip, leading Jobs to quip that “money isn’t everything” in software development.

Perhaps the most intriguing feature of Leopard is Time Machine, an application that lets users back up and restore settings and files via a 3D user interface. While the usefulness of 3D interfaces often been questioned, experts said that in the case of Time Machine, Apple had developed an intuitive system for scheduling backups.

Other features include native support for 64bit software; Spaces, which allows users to create multiple desktop settings; and improvements to email, calendaring, Dashboard and the Spotlight search tool.

In hardware, Apple released the dual-Xeon, quad-core Mac Pro desktop based on Intel’s latest “Woodcrest” generation, which completes the transition to Intel processors; and a new dual-Xeon, quad-core Xserve rack-mount server.

Mac OS X sales remain modest compared to Windows but Apple’s market share is growing rapidly on the back of Intel-based systems, attractive hardware designs and complementary products such as the iPod. Microsoft, by contrast, has been uncharacteristically weak with a stuttering software release schedule and underwhelming arguments to upgrade, leading to slow PC sales growth.

Although enterprises are likely to be last to adopt Macintosh systems, the release of software such as Boot Camp and Parallels has made it easier to run Mac OS and Windows on the same systems and Apple has perhaps its best chance in many years to dent Microsoft’s dominance on enterprise clients.

“We’ve noticed interesting improvements in Apple networking, Active Directory compatibility and other features they’re putting into the system,” said Paul DeGroot, an analyst at Directions On Microsoft. “It’s a very awkward time for Microsoft but [Apple has issues] in terms of general compatibility and it’s not clear that Apple has a mechanism for selling Macs in large quantities to business customers.”

Apple must also contend with an investigation into its accounting practices. The company has already said it is likely to restate earnings going back several years.