With the release of Mac OS X 10.7 (Lion), Apple now allows full virtualization of its operating system, provided that it is installed on Apple hardware which is also running OS X 10.7.
Apple's updated license agreement allows you to install up to two additional copies of Lion on your Mac which is already running a retail version of Lion. This does not apply for Macs that came with Lion pre-installed, as Apple's License Agreement does not allow this version to be virtualized.
You cannot install OS X 10.6 or OS X 10.5 Client (only OS X 10.5 or OS X 10.6 Server), and you cannot install OS X 10.7 on a Mac running OS X 10.6. For more information, see Apple's Software License Agreement for Mac OS X (Lion 10.7).
Note: The preceding link was correct as of September 13, 2011. If you find the link is broken, provide feedback and a VMware employee will update the link.
This article describes how to install Mac OS X 10.7 (Lion) in a new virtual machine in VMware Fusion 4. Installaing OS X 10.7 in a virtual machine is not supported versions of Fusion older than 4.0.
To learn more and to read the entire article at its source, please refer to the following page, Installing Mac OS X 10.7 (Lion) as a virtual machine in Fusion 4 (2005334)- VMware Knowledge Base - latest articles