install oracle virtualBox to Windows 7
Download Virtual Box
Go to following page to get more latest version Virtual Box for you machine.
Run setup file
Start following install wizard to setup Virtual Box.
You could do few setting for setup, but this blog didn't check anything, just default setting.
Feature after install Virtual Box
During install of Virtual Box, it'll stop network connection, but just few second, so basically don't need to worry.
Start run your virtual box
After you setup everything, if still doesn't work, check your Machine's virtual machine setting is enable.