If I install Ubuntu along side my windows 7 installation can I then boot into the Ubuntu and launch the windows 7 via the virtual box? Or does the windows OS have to be installed via the virtual box to work?
VirtualBox is a "virtual computer"; it looks like a full computer to the programs, and includes audio, video, disk drives, etc. When it starts out, it is like a brand new computer without anything installed.
If you have a Windows CD, you can install windows within VirtualBox just like installing it to a new computer; same with other Windows versions or Linux. You put the Cd in, or mount an ISO image of a CD, and reboot the virtual machine (called the "guest" OS). The host OS continues to run normally while this is happening.
But you can't run the existing windows 7 OS in virtual box, or simultaneously with Ubuntu.
Windows XP will work within Ubuntu virtualbox. This is how some gamers & other people run Windows programs.
Many people, myself included, run Windows7 programs with WINE, or PlayOnLinux, which to varying degrees of capability, might work.
Apple OS-X users have the similar problem. IMHO - to be an Apple OS-X user, you are best to avoid Apple-branded hardware because you can get better hardware components in PC and notebook world.