Virtualization software maker VMware has posted a beta of an Intel-based Mac virtual machine that will compete with Parallels Desktop, the Apple-endorsed program that lets users run Windows and Linux on Mac computers.

When it goes final, VMware's Fusion will run multiple instances of non-Apple operating systems -- including Windows, Linux, Netware, and Solaris -- on an Intel-based Macintosh simultaneously with the Mac's own operating system. That differs from Apple's own Boot Camp program, which lets users boot into either Mac OS X or Windows, but not run the two at the same time.

VMware is counting on its expertise in the Windows ecosystem to sell Fusion. "VMware virtual machines created with existing VMware products are all cross-compatible, including virtual machines created by VMware Workstation, VMware Player, VMware Server, and VMware Infrastructure 3," the developer said on its Web site.

In June, Parallels Inc. shipped its own virtual machine software, Parallels Desktop. Since then, Apple has plugged Parallels on its Web site and has stocked it in its retail stores. Two months later, VMware declared it would join Parallels in the Mac virtualization software market. The same day as VMware's announcement, Microsoft abandoned plans to update its Virtual PC product to work on Intel Macs.

Fusion requires a host Intel-based Mac with 512 Mbytes of memory (1 Gbyte recommended) running Mac OS X 10.4.7 or 10.4.8; the beta will run virtual machines powered by Windows XP Professional, Windows Vista, Ubuntu 6.10, Red Hat Enterprise Linux 4 Update 4, or Suse Linux Enterprise Server 10.

The beta can be downloaded free of charge from the VMware site; a price for the software has not yet been set.