Installing Windows 8 on Virtualbox is pretty easy.
Virtualbox is a program that allows you to install virtual disks of other operating systems (OS's) on your computer.
To do this, you must do the following:
Download whats called an .iso (Disk Image File), The download will take about a half hour to an hour but its worth it.
Check what kind of computer you have by opening the start menu, right clicking "My Computer" and clicking properties and check your System Type.
If it is 32 bit Download this file.
If it is 64 bit Download this file.
Now, Open Virtualbox, or Download it here.
Create a New OS, Call it Windows 8 (If you choose add 64 or 32 bit) and select windows in type and in version select Windows 8.
Then go to settings, storage, and then select the CD/DVD Driver and upload the .iso file.
Then, Start the System.
Enter the Product Key:
Then Windows should do the rest.
If you have any question tell me in the comments.