Well here comes DTV ready or not, all over-the-air broadcast must be digital by Feb. 17. So if you have an older TV you can check the TV or manual to see if it has an ATSC tuner. If not you need a converter box. Your old antenna, indoor or outdoor, should work for digital signal (with converter box).
Cable and satellite subscribers should have no worries except that they can now charge for more digital channels. So check it out.