identify system service 100% cpu svchost.exe

Which system service is causing svchost.exe to use 100% cpu value?

First lookup the PID (process identifier) number in task manager that is causing the problem. You may have to tell task manager to add the column.

This command will allow you to identify the problem service by showing what each svchost.exe PID is running.

C:\>tasklist /SVC /FI "IMAGENAME eq svchost.exe"

In vista you can right your problem process click and choose "go to service".