Process Explorer
If you have any deeper involvement with your computer aside from checking your AOL mail, then you’ve probably had to use Task Manager to stop a problematic program. Process Explorer is like a beefed up Task Manager, allowing you access to much more than just the currently running processes. You can track processes, the handles those processes are using (i.e. all of the directories, files, and registry keys that svchost.exe is using), and descriptions of the DLLs a process loads along with the company that made them.
Grab a copy from Sysinternals Freeware.