Hello,
You should check if the VT-x support is enabled for the virtual machine. Launch Parallels Desktop for Mac, select the virtual machine and click any link in the Configuration page. You will see Options at the very top of the list. Make sure that the Enable Intel VT-x support option is selected.Please, try to check the following:
1. Set memory for Virtual Machine to less than 1 GB
2. Perform Mac and Windows side disk defragmentation
http://www.xvsxp.com/system/system_tools_defrag.php
3. Set Adjust memory limit from Auto to Manual at Parallels Desktop -Preferences-Memory, and set limit a bit more higher than VM memory
4. Disable Themes in Windows XP serives.msc stop Themes service
5. If you are running in Coherence, try to switch to Single Window, or lower Mac resolution
6. Some antivirus software can load CPU when Heuristic Prediction is set, or Tamper protection (Symantec, MacAffey), adjust settings to risk you are supposed, high security settings is not always good idea, as it can also affect software running
7. Run msconfig , and disable unneeded startup items
See
http://www.netsquirrel.com/msconfig/msconfig_xp.html
8. Make sure that no VNC,or remote desktop connection is established to Mac, this can slowdown Parallels Desktop