The feature was previously available only in Windows Server 2008 and Windows Server 2008 R2 but now we can use it in Windows 8.
Many of us have done such virtualization before by using virtual-box or vmware workstation and other virtual solutions where some of them come free and some are commercial products but when you are using windows 8 you can use Microsoft virtual solution called Microsoft Hyper-V.
1 : open program and features which come under control panel->Programs
2 : click on turn windows feature on off seen on the left pane
3 : check Hyper-V box
|after reboot you see these two icons on your start screen|
You run Hyper-V manager
|i tested windows 7 on Hyper-V and worked fine|
Try it yourself!!