There are at least two good ways to get rid of the menu bar. One is Menufela and the other one is MenuShade.
Menufela
ninjakitten.usThis one is a $5 haxie that requires Application Enhancer (which it installs automatically). It makes the menu bar act like the Dock when it's set to automatically hide. It doesn't work well for Leopard, though.
MenuShade
www.nullriver.com...This one is free, and instead of hiding the menu bar, it puts a shade over it, dimming it. It can be set to totally black which is what you want. On a regular monitor this may look weird, but most TV sets already have black borders around the screen anyway, so you won't notice it at all. It undims when the mouse hovers over the menu bar.
PresentYourApps
www.eternalstorms.at...This is the best choice, since it requires no hacks (apart from it editing some plist files in your applications). It allows you to select what applications where the Dock and the Menu bar should be hidden. Since you won't be using so many different applications, it's easy to add Finder, Dragthing and such to the list.