PaneKiller is just as easy to use as the Start menu, but more flexible, powerful, and configurable.
Open PaneKiller's Properties and go to the Taskbar tab. Under "where do you want PaneKiller to appear?", select "as a replacement for the Start Menu." You can leave the other appearance options selected, or not, as you wish. When you click Apply, PaneKiller will take over the Start button (you will see it change).
If you haven't already, you may want to go to the Contents tab, and check boxes in the list of menu items so that PaneKiller's menu contains the same options that the Start menu usually does. Of course, this is up to you.
Now, left or right-clicking the Start button will access PaneKiller and its options. You can still access all the stuff that the Start menu had, plus much more, and you can right-click nearly anything to access its context menu. You can also drag files from the Explorer and hover over the Start button, and PaneKiller will pop up to allow you to drag and drop through the menus.
You can temporarily access the original Start menu by shift+clicking the Start button, or pressing the Windows key.
To make the normal Start menu return to being the default, either right-click PaneKiller's Start button and select "restore default Start menu", or go to PaneKiller's Properties and deselect "as a replacement for the Start Menu" on the Taskbar tab.