I can remove your taskbar 100% but you will still be able to open the Start Menu with the Windows key on your keyboard if that's any good to you.
I found the C# source code here
but it came as code for a small application with two buttons (one to hide the Taskbar and Start Button and one to show them again). I've modified the code to automatically do what you want upon running it and then it exits, it uses the Windows API so there isn't any dirty hacks involved either.
To make life easier I made it into two exe's, one does the hiding and the other one shows it again.
Simply extract the exe's to your Windows folder and create a shortcut to the 'HideTaskbar.exe' in the Start Menus 'Startup' folder to make it happen upon each bootup. HideTaskbar.zip (Requires Dot.Net 2.0 or higher) EDIT: Works for Vista too btw!