Svchost.exe is a process that runs services. Multiple services can be run by each instance of svchost.exe and there are multiple instances of svchost.exe running, so Task Manager isn't very helpful.
You can use Process Explorer:
http://technet.microsoft.com/en-us/s.../bb896653.aspx which is like Task Manager on steroids. It will display a tree view of running processes, and within svchost.exe what services are being run. You can sort by CPU usage and it can be configured to show which service being run by svchost.exe is using the CPU time.