virtualbox.org

I use Ubuntu 64 bit as my host, I have created a Centos 5.5 i386 vm, the installation appeared to have been completely successful, but now it only partially boots and hangs. After Centos starts initially it does present a menu option to edit the boot command.

Any ideas as to what the problem can be?

Sounds like you need to edit the boot sequence and add the divider=10.
Google divider 10 CentOS to see how to do it