Uncompressing Linux.... 0k, booting the kernel
The problem is that virtualbox is incapable of handling some of the SMP kernel options when you start the kernel. Currently a bug is reported at Sun to fix the problem. A workarround for this problem is to boot the Enterprise-up (2.6.9-220.127.116.11.1.EL) kernel instead of the Enterprise (2.6.9-18.104.22.168.1.ELsmp) kernel.
It is not the best workarround but you can get a OEL system running in a virtualbox. When you like to default the system to start with this kernel you have to edit the file /boot/grub/grub.conf and change the default=0 to default=1. In my case the 1 is the Enterprise-up (2.6.9-22.214.171.124.1.EL) kernel which can start with virtualbox.