virtualbox.org

As an experiment, I decided to upgrade through every version of Windows. When I installed Windows XP, and put in Windows Vista , there was no upgrade option. It forwarded me to the terms and conditions, and then went straight to the hard drive list. The VM's running Windows XP SP3, with 3072MBs of RAM allocated, PAE/NX, and VT-x/AMD-V enabled.
Any help would be great!

I guess you can't upgrade then. Ask Microsoft, as this has absolutely nothing to do with VirtualBox.