If you don't have the integrated tuner, you'll need a box. But, if you're going with satellite or digital cable vs. OTA (Over The Air), you'll need a box anyway.
Just like any other tv, you can still use it with any signal. When you go shopping, make sure to have the salesperson show you non-HDTV channels. Find the one with the best line doubler to get the best picture; most channels are non-HDTV, so that's what you'll be seing the most.