If your favourite Linux is not in the compatibility list, the first thing to do is to check that there is no pending request for it in the Feature Request section.

If there is no feature request, you can open a new one AND use Submit a Linux section to fill in all the information needed to add your Linux to the support list.

Filling in the whole Submit a Linux form will greatly increase the chance of your Linux to be added.

Be aware that some Linux are not added because of technical issues as is currently the case for Mandriva (need an initrd patch), OpenSolaris and OpenSuse (don't work in VirtualBox 3.1.2)...