The Task Manager/Processes list needed applications running for XP to run. The list shows memory and CPU usage. System Idle Process means just that. This will decrease as needed applications command the CPUs' attention.
Go to Help and Support in windows. In search type "Task Manager". Here you will find information about the Task Manager.
These web sites define smss.exe
If you are not getting this information from the Task Manager but from a third party free Memory Manager, you have pests. For pest removal see,
others will follow with other points,
What does it mean when it says my system idle process is low or when my smss.exe is above normal?
Do I need to adjust to normal and if so, how?