Install Tiger in VMware Fusion
This article references VMware Workstation 6 as being able to run OS X with some hacks, but it's slow. But more importantly, that article runs down what I thought was the only known solution to running OS X in a VM: VirtualBox. So you aren't going to be able to do this with Fusion, but you can do it with VirtualBox.

Also: Apple does allow virtualization of OS X Server (check the date on that article - circa 2007). It honestly wouldn't stand much of a chance in the big, corporate IT world if it couldn't be legally virtualized these days.