Both Parallels and VMWare Fusion offer "migration" programs that will attempt to transfer the Windows PC into a new Virtual Machine on the Mac if the Windows PC is on the network. That machine generally will boot just fine.
HOWEVER the problem that will arise comes from Microsoft's licensing. If you have an OEM version of Windows on the old PC (which 99% of users will, since they buy a Dell, Lenovo, etc. with Windows pre-installed) the OEM version is licensed only to run on that *ONE* CPU. Thus when you try and boot that machine it will boot, but Windows will not be able to authenticate the license. Microsoft's servers will discover you have "moved" the system to a new CPU.
At that point you *might* be able to figure out how to buy a license from Microsoft that the Windows machine can recognize. I did get Microsoft support to help with that once, but it was a bit of a convoluted process. The problem isn't buying the license--that's easy. The problem is getting the version of Windows you have to accept the license number and register itself.
As well, sometimes Microsoft has been known to offer a "become legal" option when faced with an unauthorized copy and may offer to sell you authorization. If you get that dialog things are a lot simpler :-) .
If you actually orignally installed a "retail box" version (not an OEM) of Windows on the original machine then you won't have any of these problems, as that license *can* be transferred to new equipment. The program will still want to reauthenticate but Microsoft will give your copy the "OK" once it confirms the license and finds it's a full retail license. Note that OEM versions are available for stand-alone sale, theoretically for those building their own system, so just the fact you bought it from NewEgg doesn't mean it was "retail"--retail versions come in retail packaging (fancy box), while OEM version tend to come simply in mailing sleeves.
Office is also sold both ways, though more users have the retail version. But if you bought Office with your Windows PC then you may find that license also cannot be transferred and you'll have to buy a new version of Office for the Windows virtual machine. Various other Windows software may have licensing quirks you'll run into with a transfer.
With full retail licensed copies of the Microsoft software, the process is dirt simple. But, as I said, Microsoft doesn't sell most of the copies of Windows that way, rather selling "one machine" linked versions of the operating system that can't be moved to new machines.
The advantage of the transfer is clear--if you do it, you skip the whole mess of having to reinstall all of the software and rebuild the Windows machine from scratch. Unfortunately Microsoft offers nothing like the Migration Assistant. The disadvantage is the same as using the Migration Assistant--you end up "inheritiing" various issues, along with the setup, from the old machine and transfer that onto the new one.
Note, as well, that you really are in no worse shape (and potentailly better shape) than if you had bought a new Windows PC.
