I have installed RHEL 5.5 on VIrtual Box and Host system is Ubuntu 12.04. I can access the files of Ubuntu by using the sharing services of Virtual Box.
But how can i access the files of RHEL which is installed on Virtual Box??????
Virtual Box Shared Folders provide access to host directories from a guest OS. This does not work the other way, i.e. accessing guest directories from the host.
To do so you may want to access file across a virtual network using SSH or Samba. See this questions for more (it should be the same for RHEL):