I tried to install windows xp in kvm on fedora 12. The result was a very very slow windows xp virtual system. After some tinkering, I think I found my problem. My fedora 12 is x86_64 so the virtual machine defaulted to emulating x86_64. When creating the virtual machine instance, change it to i686 instead under the advanced settings. Everything ran 10 times faster once I reinstalled the virtual machine instance like that.