This utility is excellent for looking at what processes are running on your system. It will show you not only processes but threads that the Task Manager often hides from you, including spyware. It also can give you details on each task and kill them, if you so wish.
Installation doesn't modify the Windows Registry, so you simply extract it to wherever you want. I find it so useful that I put a shortcut to it in my Startup folder; I run it with Windows.