The flaw, which affected thevirtualmachine monitor (VMM) in Virtual PC, could enable an attacker to use applications running in user-space on a guest OS to access portions of theVirtual PC memory that should be inaccessible to those applications.
Once you've installed these "virtual" machines on your Mac, you can for the most part install PC applications on thevirtualmachine as though it were a real PC--though few software vendors will actually help you out running their software in an emulated environment.
The performance of a virtualmachine, for example, may vary widely, based on the computing taking place on the other virtual machines that are running on the same physical machine.