Apple is working with Microsoft and Intel to develop a VMWare like virtualization software for Mac OS X 10.5 called Chameleon.

Apple Chameleon will allow Mac users can run multiple operating systems (like Windows XP, Vista or Linux) simultaneously on a single Intel-based Mac.

While Booting Windows XP on Intel Macs is now possible, Chameleon would prevent the need for rebooting to use a particular application.

Mac OS X v10.5 Leopard is expected to be released early 2007, roughly around the same time Microsoft would release Windows Vista.

Microsoft currently develops Virtual PC for Mac that lets you run Windows Software like Visio or Macromedia Dreamware on a Mac computer. VirtualPC is available for Panther and Tiger (Mac OS X version 10.3 or 10.4).

Once Chaemeleon is public, Microsoft may cease to develop Virtual PC for Intel-based Macs. VMware Workstation virtualization software is another popular virtual machine suite for Intel x86-compatible computers.

Source: Apple Chemeleon VMWare