o_O
WMWare is not an emulator. If anything, it should be called a virtualizator. Emulation is quite different.
But I take it you mean you want to run another PC inside your PC, so to speak. A virtual OS. That's what these kinds of products were designed for.
It really depends on your needs. I think there used to be some free WMWare version, but generally it's quite complex. Microsoft also has their own--Microsoft Virtual PC or something. Long ago since I used it last, so I don't know how it works today.