If your laptop does support hardware-assisted virtualization (HAV) , you can easily install virtual box and try windows8 without effecting windows 7 at all.But every PC has not CPU hardware virtulization function enabled or not supported. So before install windows 8 in virtual box you must check your system whether support hardware virtualization or not?
How to Check That My Laptop Support Hardware virtualization ?
If you never check it and don’t know about it then may be you will not successful to install windows 8 developer preview in virtual box. After checking if you have found that your PC never support hardware virtualization then skip testing windows 8 on virtual box. What you can try to do if you are eager to know even you cant install is try to partition your hard drive and install windows 8 from there in a new partition drive. It will work fine. So do you like to check that your laptop does support hardware virtualization or not just go Windows utility and install the havdetectiontool.exe file. Run it may be you will be prompt for giving windows administration password just give it and you will see a message like this picture below: