I tried to install Fedora 18 64 bit on my Virtual Box running on 64 bit windows 8 every time it failed with errors..
Finally I tried downloading 32 bit version and it got installed fine.
Only issue I faced is with the Install Virtual Box Guest Additions because unless other Debian based distributions Fedora does not install developer tools by default.
enter your root password
yum update kernel*
yum install gcc kernel-devel kernel-headers dkms make bzip2