The system is very slow to do anything, even browse a local folder, and CPU sits at 100% frequently. Guest is XP 32 bit. Host is Scientific Linux 6.2, Libvirt 0.10, Guest XP OS shows ACPI Multiprocessor HAL and a virtIO driver for NIC and SCSI. Installed.

 CPUInfo on host:
 processor       : 0
 vendor_id       : GenuineIntel
 cpu family      : 6
 model           : 42
 model name      : Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
 stepping        : 7
 cpu MHz         : 3200.000
 cache size      : 8192 KB
 physical id     : 0
 siblings        : 8
 core id         : 0
 cpu cores       : 4
 apicid          : 0
 initial apicid  : 0
 fpu             : yes
 fpu_exception   : yes
 cpuid level     : 13
  wp              : yes
  flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat         pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc   arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
  bogomips        : 6784.93
  clflush size    : 64
  cache_alignment : 64
   address sizes   : 36 bits physical, 48 bits virtual
    power management:


 <memory unit='KiB'>4194304</memory>
 <currentMemory unit='KiB'>4194304</currentMemory>
 <vcpu placement='static' cpuset='0'>1</vcpu>
 <os>
 <type arch='x86_64' machine='rhel6.3.0'>hvm</type>
 <boot dev='hd'/>
</os>
<features>
 <acpi/>
<apic/>
<pae/>
</features>
<cpu mode='custom' match='exact'>
  <model fallback='allow'>SandyBridge</model>
<vendor>Intel</vendor>
<feature policy='require' name='vme'/>
<feature policy='require' name='tm2'/>
<feature policy='require' name='est'/>
<feature policy='require' name='vmx'/>
<feature policy='require' name='osxsave'/>
<feature policy='require' name='smx'/>
<feature policy='require' name='ss'/>
<feature policy='require' name='ds'/>
<feature policy='require' name='tsc-deadline'/>
<feature policy='require' name='dtes64'/>
<feature policy='require' name='ht'/>
<feature policy='require' name='pbe'/>
<feature policy='require' name='tm'/>
<feature policy='require' name='pdcm'/>
<feature policy='require' name='ds_cpl'/>
<feature policy='require' name='xtpr'/>
<feature policy='require' name='acpi'/>
<feature policy='require' name='monitor'/>
<feature policy='force' name='sse'/>
<feature policy='force' name='sse2'/>
<feature policy='force' name='sse4.1'/>
<feature policy='force' name='sse4.2'/>
<feature policy='force' name='ssse3'/>
<feature policy='force' name='x2apic'/>
 </cpu>
 <clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup'/>
</clock>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/libexec/qemu-kvm</emulator>
<disk type='file' device='disk'>
  <driver name='qemu' type='qcow2' cache='none'/>
  <source file='/var/lib/libvirt/images/Server-10-9-13.qcow2'/>
  <target dev='vda' bus='virtio'/>
  <alias name='virtio-disk0'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</disk>