Hello,
some performance tips:
1. Set memory for Virtual Machine from 1 GB to 1.5 Gb, video memory to at least 128, disable 3D acceleration (if not using 3D applications), adjust Optimization settings (Configure -> Optimization)
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