The general recommendation to this is, don't do it. Two reasons: First, if the copy of windows that you have on your PC came with it, you can't legally virtualize it. That means you have to buy a copy of windows anyway. Once you do that, you're almost always better off building a virtual machine from scratch and reinstalling your software and documents. Converting a PC results in a bloated, buggy, unstable virtual machine.
If you decide to take the risk, the best option is to download the standalone VMWare Converter, plug in a USB external drive into the PC, and use it to create a virtual machine (doing it from a live PC across the wire often fails). Then you can just plug the external drive into the mac and copy the virtual machine to that hard drive.
Here's the link to the converter: Download VMware vCenter Converter Standalone for P2V Conversion