"This is a very good public link to read about service control manager internals and how to manage services.
Description of svchost.exe http://support.microsoft.com/kb/314056
for troubleshooting purposes if we want to isolate any one service running under svchost---we can do that using sc config BITS type= own
now as you see BITS is running under its own scvhost process.
This is like a two for one deal...
First there's a link to the cool Managing System Services document (87 page chapter 13 from what I think is the Windows Server 2003 Resource Kit)
And then there's the tip on how to isolate a Service in a svchost.exe instance. (Say because a SVChost.exe instance is chewing up processor cycles, but that instance is hosting a number of services so it's hard to tell which one is being bad. So you want to isolate each service to its own svchost instance to hunt the evil one...)