You don't have to dual boot. You can run one OS inside a virtual machine. The two most popular free VM programs are VMWare Player and VirtualBox. That'll let you run Windows 7 inside a window under Windows 8 (or vice versa). Performance is impacted, especially for 3D apps, but most apps run at an acceptable speed. Audio usually runs ok, though sometimes it stutters.
I'm biased towards VMWare since I use VMWare Workstation, but for the free versions VirtualBox supports snapshots while Player does not. (VirtualBox OTOH reacts badly to moving/copying the VM files while VMWare has little problem with that). Both also support a mode where an app running in the VM shows up on your regular desktop as if it were a native app. It's a bit clumsy and slower than running inside a window, but if that's what you need, it's possible.
You might also want to look at VMWare Convertor. That'll take an existing computer and turn it into a virtual machine which can be run on either VMWare Player or Virtualbox. I do that every time I get a new computer now - convert the old one to a VM and put it on the new one. That way for the first month or two after I switch, if there's something I forgot to copy/transfer, I can just start up the VM and access it that way.
http
/www.vmware.com/products/player/
https
/www.virtualbox.org/wiki/Downloads