How to reinstall windows from created system recovery media, in case dell datasafe not available?

Hello,

I am installing windows 8 Release preview, but soon windows 8 RTM will be available & am looking forward to switch to the windows 8 Final Version. As per the terms of microsoft i can't install windows 8 pro from the release preview, for that i need to Reinstall the legal prior windows copy (in my case windows 7) for that i created System recovery media (Usb) on my dell studio laptop from Dell Datasafe local backup to reinstall the factory image. My question is after being on release preview (Win 8) Dell datasafe will be unavailable, in that case how to re-install windows 7 back from recovery media (usb) how to boot it?