How to solve the problems of "Oracle Enterprise Linux" in virtualbox

Not able to boot:
Just press escape during the grub loading process and choose the second kernel :), that's it! If you want it to be persistent to avoid doing that at every startup, just go edit the "/boot/grub/grub.conf" and change "default=0" to "default=1" to point to the second kernel automatically.

Source

Not able to install Guest Additions:

1. mount the installation DVD, navigate to the folder "Server" and issue the command "rpm -ivh kernel-devel-2.6.18-164.el5.i686.rpm"
2. unmount the DVD (if you're not able to unmount due to a bug in virtualbox that prevents unmounting, just shutdown the guest OS and then remove it from the storage section)
3. In the guest OS, click "Devices"->"Install Guest Additions"
4. The CD will be mounted, navigate to its folder (in /media/VBox***) and run "sh VBoxLinux***x86.sh" (x86 here if you're using 32-bit edition)
5. Reboot and enjoy :)