Depends on a few things, you'll probably have to find a lower resolution that conforms to the aspect ratio of your TV. For example, if it's widescreen it'll be 16:9 I think, so if you divide the width of the resolution by 16, then multiply by 9, you'll get the height.
Do you know what the native resolution of your TV is? What type of HD does it support? What type of connection are you using? Is it a new or older Macbook? Information is power 🙂