The only way to do this would be to completely and entirely stop using Windows Explorer, and use a custom shell to replace explorer completely. This means you would no longer have the usual start menu, explorer windows, etc, and would have to rely entirely on some other piece of software for browsing your file system. Some people do this, and there are replacements available, so if you really want to completely eliminate the windows taskbar, find and use one of these of your choice. There is already a SuperUser question discussing the various options.
In order to completely replace explorer, and have your replacement be the default shell which opens up when you log in, create a
REG_SZ value called
[HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon] using the registry editor. This will completely replace explorer for your account, making it unnecessary to use any taskbar hiding/killing techniques.