I installed xen under openSUSE 12.1 and tried to create a Windows XP VM. I got the error “The processor(s) in this machine do not support full virtualization.” I am using a modern machine with an intel i5-2400S processor. Looking at the processor flags when running under the normal (not xen) operating system, /proc/cpuinfo shows the vmx flag (permitting full virtualization) for all cores, but when I boot under xen, I get a much shorter list of flags which does not include the vmx flag. What gives? How do I get full use of the CPU and how do I install windows under xen?
Did you try looking for these options in the bios and enabling them ?