Long back I had shown How to Fix svchost.exe Memory Hogging Issue. It is still one of the most viewed posts on Technically Personal! Now, this is a supplementary article to that post which helps you analyze and understand SvcHost.exe process in a much better way. I suggest you to read the parent article (link given above) to understand what svchost.exe is and its relevance.
The Svchost Viewer is a small application that lists all of the current svchost.exe instances. It also shows how much memory each one is using and what services are running underneath it.
How to use SvcHost Viewer?
Svchost Viewer is it requires no installation and can run directly off your USB flash drive, coming in handy when troubleshooting. Just double-click on the application to launch, and then click Yes when prompted whether to get the data. After taking a few moments to complete the scan you will be presented with the number of svchost.exe instances running along with the service name, description, memory usage, and program path.
Svchost Viewer is open source, requires the .NET 2.0 framework and should work on Windows XP (SP2), Vista and Windows 7.