Understood. If you follow Chapter 7.1.3. Step by step: creating a virtual machine on a headless server set-by-step you should be able to create this. I know I have done it this way several times although it failed for me at first due to syntax errors I inserted. But since I figured it all out I do this maybe once a month now at various locations. Think the steps through of what they are really doing and I bet you get it.
Here it is cut down with only the steps.
Headless install (access host via ssh or terminal if you are doing this local) Replace names as required. Remember what you are doing is building a virtual computer with virtual parts.
- 1. VBoxManage createvm --name "Windows XP" --ostype WindowsXP --register
2. VBoxManage modifyvm "Windows XP" --memory 256 --acpi on --boot1 dvd --nic1 nat
3. VBoxManage createhd --filename "WinXP.vdi" --size 10000 --remember
4. VBoxManage storagectl "Windows XP" --name "IDE Controller" --add ide --controller PIIX4
5. VBoxManage storageattach "Windows XP" --storagectl "IDE Controller" --port 0 --device 0 --type hdd --medium "WinXP.vdi"
6. VBoxManage openmedium dvd /full/path/to/<iso>.iso
7. VBoxManage storageattach "Windows XP" --storagectl "IDE Controller" --port 0 --device 1 --type dvddrive --medium /full/path/to/<iso>.iso *
8. VBoxHeadless --startvm "Windows XP"
For a real CD/DVD VBoxManage storageattach "Windows XP" --storagectl "IDE Controller" --port 0 --device 1 --type dvddrive --medium Host:/dev/sr0 *
Edit: I just saw your reply as I was previewing my reply.
You may not need to go that far as to start over. I think at one time I went the route you did, can't be sure though since it has been so long ago, but try deleting the guest and starting over there first.