1. Start, Run..., cmd.exe, systeminfo.exe, then search for system manufacturer, and if virtual it will be listed as follows :-
If this is a VMware virtual machine, result should be:
System Manufacturer: VMware, Inc.
System Model: VMware Virtual Platform
If this is a Hyper V or a Microsoft Virtual PC machine the result should be like this:
System Manufacturer: Microsoft Corporation
System Model: Virtual Machine
2. Start, Run..., msinfo32.exe - basically a graphical user interface showing much the same information as you get from method 1.