You have the Home Switcher app installed? Have you opened it up, set as default, and then press launch for Launcher Pro? That should work. In Launcher Pro's Preferences under Behavior settings, what do you have set for "Home Key action"? I have mine set for "open/close screen previews". Whatever you have set in that setting should happen when you press the Home key.
Other than that I'm not sure what the problem could be. You could try uninstalling Launcher Pro and re-installing the latest version from the market and see if that fixes it. Or also go into "Manage Applications" in your phone's settings and clear the defaults for Launcher Pro and then reset it to default in Home Switcher and launch it.
Good luck.