I am running Windows 7 and put Ubuntu 12.10 on my computer. I want to be able to switch between the 2 with out having to reboot and also be able to access some files saved in Windows from Ubuntu and the other way around. I was told VirtualBox would be the way to do this. I installed it from here https://www.virtualbox.org/wiki/Downloads and set it up the best I could from the instructions in the installer and what I read online. But I cant figure out how to switch from one OS to the other with out rebooting or how to share files.

For sharing files, some things I read said something about having to set up part of virtualBox on the guest OS, so do I need to reboot and also download it on Ubuntu for any of this to work?

Could someone please either give me some simple instructions on how to get both of these things to work or tell me somewhere that has some simple clearer instructions because what I have found so far was not very clear to me on what I needed to do.

Also when I click start in virtualBox in Windows for my Ubuntu system I get "FATAL: No bootable medium found! System halted." which clearly is part of the problem I just don't know what it means.

Thank you!