If Windows Task Manager doesn't offer you enough of a break-down of your system processes for you, this Free Extended Task Manager might be what you're looking for.
Basically, 'extended' is exactly what it says it is. It's a slightly larger, very similar-looking task manager, with slightly extended features.
If you open the Performance tab, and hover the cursor over the graphs, you can see CPU usage at any point in time and view the programs that are sucking up the most processing power.
The Network Port tab shows you who is connecting to you, and who you are connecting to, including IP addresses. The Applications tab gives you big icons instead of the usual list, which is a much friendlier look than in Windows Task Manager.
There are more features including a file lock finder which finds out why a particular file cannot be deleted, and 'unlocks' the process, which is a useful tool.
There is nothing that makes Free Extended Task Manager particularly special - it is no easier to use than the built-in task manager - but its extended features are useful and the utility is free.
Overall, Free Extended Task Manager is a stable and fairly comprehensive utility great for anyone interested in the more mysterious workings of their PC.