Yesterday Apple released Mac OS X 10.5.6 update. For folks who are running Mac OS X Server 10.5.x in a virtual machine, you may see Software Update (in the virtual machine) offering to update your system. We recommend that you do not proceed with this update, or at least take a snapshot of your OS X guest first.
are some known issues with this OS update that cause WindowManager to fail under default setting in a OS X virtual machine, as well as some USB issues. Go to the updated VMware Fusion 2.0.1 Release Notes
for more details on these issues and
workaround in case you already updated your virtual machine to 10.5.6.
These issues will be fixed in the next maintenance release of VMware Fusion. And they do not affect Mac OS X 10.5.6 as a host.