Well, darn, there goes that idea. As far as I know, there is no Group Policy for Home Edition (that's what you have, right?). It's a long shot, but you can try opening your Control Panel and going to Taskbar And Start Menu. Click on the Start Menu tab then go to Customize and see if you can find any options that let you disable Log Off and Shut Down. I don't believe Professional has it (mine doesn't), but I know that some versions of Windows do. In the meantime, I'll see if I can find any other suggestions.
There's a way to edit your registry to get rid of the options, but the drawback is that it disables the commands so that you can't even shut down from the Task Manager.