Just download VirtualBox.
* VirtualBox: free, available for Windows, Mac, and Linux; the tongue-in-cheek mention of Linux earlier is because VirtualBox is also distributed by some Linux repos, so if you happened to be using one of those flavors of Linux, you can just get VirtualBox via their repo (but that's all irrelevant since you're using Windows, in which case, you go to the VirtualBox website to grab the installer)
* VMware Workstation: has the most features; not recommended because it's expensive and most people don't need all those extra features (I use a lot of VMs, yet I still don't see a reason to ditch VirtualBox for VMware)
* Virtual PC: Microsoft's solution, available for Windows 7. I don't recommend it because it's been abandoned (not available for Windows 8) and because it can't do things like run a 64-bit guest OS.
* Hyper-V: Microsoft's "replacement" for Virtual PC. Requires Windows 8 (or a Server edition of Windows). Also not recommended because it's a type 1 hypervisor, and what you really want is a type 2 hypervisor (which is why I put "replacement" in quotes since Virtual PC was type 2, but Hyper-V is type 1).